Second Hinode Science Meeting
Beyond Discovery – Toward Understanding
29 September- 3 October 2008
Boulder, Colorado USA
Abstracts
Authors: : Lucia Abbo and Alan GabrielTitle: Coronal hole study through the solar atmosphere: from the chromosphere up to coronal layers
Abstract: We analyse intensities and velocities over a range of temperatures, covering the chromosphere to the corona, within polar coronal holes. Using observations from EIS and SOT on Hinode and CDS on SOHO, we examine the velocity fields over this region of the lower corona, with the aim of better understanding the onset region of the fast solar wind during the current solar minimum period. Existing observations are being studied and newer observations are currently under way.
Session: Source of the Solar Wind/CME
Authors: : Tayeb Aiouaz
Title: Evidences of Relentless Reconnections at Boundaries of Supergranular Network Lanes
Abstract: Doppler-shift properties of the solar transition region (TR) and low corona are investigated in relation to the underlying chromospheric supergranular network, with particular regard to the role of the magnetic field. EUV line properties were obtained from a large raster scan of the solar transition region and corona acquired by the UV/EUV spectrometer SUMER on board SOHO. The observed regions include an equatorial coronal hole, as well as surrounding quiet Sun areas. I present correlations between the chromospheric network, and the N IV (765.15 Â), O IV (790.19 A), S V (786.50 A), O V (760.45 A) Doppler shifts in quiet Sun and coronal hole. It is established that the maximum inflow (redshift) at transition region temperatures appears statistically toward the center of the network lanes in the quiet Sun areas and toward the boundary of the network lanes in the coronal hole part. Furthermore, while the strong red-shifts in the TR lines complement spatially blue-shifts from the low corona (Ne VIII, 770.41 A) in a puzzle-like pattern, bi-directional flows (i.e. cospatial strong red/blue-shits in the TR/Corona) appear predominantly in the coronal hole. The bi-directional flows happen almost systematically at boundaries of magnetic field concentrations when compared to the reconstructed magnetogram from a MDI/SOHO series. These results allow to propose for the first time a coherent interpretation involving a single driver for almost thirty years of unexplained statistical Doppler shift variations in the transition region and corona for quiet Sun and coronal hole. The proposed scenario involves reconnections between the strong network magnetic field and continuously advected weak field from the supergranular cell interior.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Author: : Richard Altrock
Title: Solar Torsional Oscillations and Their Relationship to Coronal Activity
Abstract: Torsional Oscillations (TO) were first observed on the surface of the Sun as waves of small deviations from differential rotation, which propagate from high latitudes to the equator over solar-cycle time scales. More recently they have been inferred from observations of solar global oscillations to occur in the convection zone. Long-lived brightenings in the corona have also been observed to propagate from near the poles to the equator over similar time scales. This paper will discuss the relationship between TO as observed on the solar surface and in the convection zone and brightenings in the corona. We find that there is an apparent connection between these two phenomena that extends from the equator to latitudes as high as 70 to 80 degrees. This may imply control of both of these phenomena by the driver of the solar cycle (the solar dynamo) and thus place observational constraints on dynamo models. R. C. Altrock was supported by the Air Force Office of Scientific Research.
Session: Bringing Modeling and Obvservations Together
Author: : Spiro K. Antiochos
Title: CME Initiation
Abstract: Coronal mass ejections are the largest and most energetic form of transients that connect the corona to the solar wind. They are critically important both for understanding the physical mechanisms of explosive solar activity and for predicting space weather. It is now widely accepted that CMEs/eruptive flares represent the explosive release of magnetic energy stored in the corona., but the initiation process is still far from understood and is currently a topic of intense debate. In this presentation I will review CME theories and present the latest results from 3D numerical modeling of CME initiation. I will focus, in particular, on the breakout model, but many of the results hold in general. The implications of these results for understanding coronal/solar wind structure and dynamics and for interpreting the Hinode observations will be discussed.
This work was supported in part by the NASA HTP, SR&T, and TR&T programs.
Session: Bringing Modeling and Obvservations Together
Author: : Patrick Antolin
Title: Predicting observational signatures of coronal heating by Alfvén waves and nanoflares.
Abstract: Alfvén waves can dissipate their energy by means of nonlinear mechanisms, and constitute good candidates to heat and maintain the solar corona to the observed few million degrees. Another appealing candidate is the nanoflare-reconnection heating, in which energy is released through many small magnetic reconnection events. Distinguishing the observational features of each mechanism is an extremely difficult task. On the other hand, observations have shown that energy release processes in the corona follow a power law distribution in frequency whose index may tell us whether small heating events contribute substantially to the heating or not. In this work we show a link between the power law index and the operating heating mechanism in a loop. We set up two coronal loop models: in the first model Alfvén waves created by footpoint shuffling nonlinearly convert to longitudinal modes which dissipate their energy through shocks; in the second model numerous heating events with nano flare-like energies are input randomly along the loop, either distributed uniformly or concentrated at the footpoints. Both models are based on a 1.5-D MHD code. The obtained coronae differ in many aspects, for instance, in the flow patterns along the loop and the simulated intensity profile that Hinode/XRT would observe. The intensity histograms display power law distributions whose indexes differ considerably. This number is found to be related to the distribution of the shocks along the loop. We thus test the observational signatures of the power law index as a diagnostic tool for the above heating mechanisms and the influence of the location of nanoflares.
Session: Perspectives on the Physics of Coronal Loops
Authors: : I. Arregui, J. Terradas, R. Oliver, J.L. Ballester
Title: Damping of fast magnetohydrodynamic oscillations in quiescent filament threads
Abstract: High-resolution observations provide evidence about the existence of small-amplitude transverse oscillations in solar filament fine structures. These oscillations are believed to represent fast magnetohydrodynamic (MHD) waves and the disturbances are seen to be damped in short time-scales of the order of 1 to 4 periods. We propose that, due to the highly inhomogeneous nature of the filament plasma at the fine structure spatial scale, the phenomenon of resonant absorption is likely to operate in the temporal attenuation of the observed motions. By considering transverse inhomogeneity in a straight flux tube model we find that, for density inhomogeneities typical of filament plasmas, the considered mechanism provides decay times of a few oscillatory periods only, thus consistent with the observed time-scales.
Session: Bringing Modeling and Obvservations Together
Authors: : Markus J. Aschwanden
Title: Heating and Cooling of Coronal Loops (Invited Talk)
Abstract: The physical evolution of impulsively-heated coronal loops and their subsequent cooling is now explored in great detail, using multi-wavelength data in soft X-rays and EUV, in particular with HINODE/EIS, XRT, STEREO/EUVI, TRACE, and RHESSI. With stereoscopic triangulation we can reconstruct the 3D geometry of active regions with unprecedented detail, comprising up to 105 loops per active region. Using some newly developed analytical approximations of the density n(s,t) and temperature evolution T(s,t) of impulsively-heated coronal loops we are now able to reproduce the observed evolution of light curves in soft X-rays, hard X-rays, and EUV and to quantify their non-equilibrium dynamics in terms of a common framework, arriving at a unified model of their hydrodynamic evolution.
Session: Perspectives on the Physics of Coronal Loops
Authors: Raphael Attie, Davina Innes
Title: Coronal heating from not-so-quiet-Sun explosive events.
Abstract: Coaligned observations between Hinode and Soho were made from the photosphere to the lower corona in the quiet Sun. We present a new description of the couplings between the plasma and the magnetic field during small explosive events. They are first detected using transition region lines in SUMER/Soho spectra and in X-ray images with XRT/Hinode. Photospheric flows are then calculated using the FG-SOT/Hinode images of the granulation in Blue Continuum. They are compared with the magnetic data from both MDI/SoHo and SP-SOT/Hinode. In this way, we reveal another contribution of quiet-Sun eruption events in coronal heating.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Author: :Deborah Baker
Title: Upflows in an active region-coronal hole complex - enigma or CME precursor?
Abstract: We investigate the plasma flows resulting from the interaction between a mature active region (AR) and a surrounding equatorial coronal hole (CH) observed by Hinode's EIS, XRT and SOT instruments from 15 to 18 October 2007. For the first 3 days, EIS velocity maps showed outflows at the AR's eastern and western edges which were consistently between 5 and 10 km/sec whereas downflows of up to 30 km/sec were seen in AR loops. However, on 18 October, velocity profiles of hotter coronal lines (Fe X, Fe XI, Fe XII and Fe XIII) reveal an intensification in outflow velocities of up to 16 km/sec at the AR's western footpoint 6.5 hours prior to a sigmoidal CME eruption. We compare the AR's plasma flows with both 2.5D and 3D MHD numerical simulations of the scenario, finding that slow jet-like outflows on the eastern side are a direct consequence of reconnection between the AR's closed loops and the oppositely oriented open field of the surrounding CH. A by-product of the reconnection is flows along the newly opened field lines on the AR's western side, driven by an increase in the gas pressure gradient resulting from reconnection of dense loops and evacuated field. We believe the intensification of outflow velocities observed at the AR's western footpoint to be caused by an increase in the gas pressure gradient as lower-lying (?) denser loops reconnect with the CH open field, weakening the overlying field above the AR filament and setting the stage for eruption.
Session: Bringing Modeling and Obvservations Together
Authors: : Balmaceda, L.A.; Domingo, V.; Cabello, I.; Palacios, J.
Title: Observations of magnetic elements in the quiet Sun internetwork
Abstract: The study of the radiative properties of small-scale magnetic elements in the quiet Sun internetwork such as bright points (BPs) is of great interest to understand, among other things, their relevance in the context of solar irradiance variations. In the last few years the observation and study of BPs has undergone great progress. However, some properties such as their magnetic field strength and other physical parameters could not yet be fully determined and it is necessary to extend this study to different times during the solar cycle. The advent of Hinode data offers a great opportunity to carry out this kind of studies. Following this line of research, we present here the analysis of high-resolution images of the quiet Sun at disk center taken with the Solar Optical Telescope (SOT) on board Hinode in the CN line (388.35 nm), Ca II H (396.85 nm) and magnetograms in the Mg I line (517.27 nm). These observations are complemented with data from the Swedish 1m Solar Telescope (SST). All data sets were obtained during the Hinode/Canary Islands joint campaign in September, 2007. In particular, we investigate the morphology, contrast and magnetic properties of BPs in a first attempt to estimate their contribution to irradiance variations. The comparison with double-gaussian models for contrast and radiative flux in BP's is also presented.
Session: Solar Magnetic Activity
Authors: D. Banerjee, David Pérez-Suárez & J. G. Doyle
Title: Plumes and Inter-plumes as seen from EIS/HINODE
Abstract: Fast solar wind originates from the polar coronal hole regions. Plume structures are seen in the off-limb corona. It is not clear that if the plumes or the inter-plumes are the preferred channels for the acceleration of the fast wind. To characterize the properties of plumes and inter-plumes we use raster data obtained with the EUV Imaging Spectrometer onboard Hinode. Density sensitive line ratios of \ion{Fe}{ xiii} 203.82/202.04 and\ion{Fe}{ xii} 186.88/195.12 together with corresponding CHIANTI atomic data are used to calculate the density. Full-Widths-at-Half-Maximum and Doppler maps are obtained from the strongest\ion{Fe}{ xii} 195.12 AA spectral line. Using the line width variation of spectral lines with height, one can also try to identify the presence waves as they propagate out of the sun. The characteristic properties of these waves can also be studied while studying the variation of line widths. Some new results from EIS on HINODE on this subject will be also presented.
Session: Source of the Solar Wind/CME
Authors: Helena Becher
Title: Inversions of Stokes profiles
Abstract: We present inversions of Stokes vector profiles obtained by the Hinode SOT/SP instrument and the ground-based SOLIS VSM instrument and inverted with the publically available HAO inversion code LILIA written by Hector Socas-Navarro. This code is based on SIR (Stokes Inversion based on Response functions), which produces a height dependent atmospheric model and uses a non-linear least-square fitting technique. Both instruments use the 630.15 and 630.25 nm Fe-lines and have high temporal and spatial resolution as well as a polarimetric sensitivity approaching 10e-4. We derive the full magnetic field vector for several time series and study the dynamic properties of the magnetic field.
Session: Solar Magnetic Activity
Authors: L.R. Bellot Rubio
Title: Sunspot magnetic fields near the diffraction limit: the Hinode view (Invited Talk)
Abstract: Thanks to the Hinode satellite it is now possible to distinguish bright and dark penumbral filaments in spectropolarimetric maps of sunspots. This important achievement helps us isolate the various magnetic components of the penumbra and characterize their physical properties more reliably. Here I will describe recent results from Stokes inversions of sunspot measurements taken by Hinode/SOT. In general, the observations confirm the scenario of large (sometimes supersonic) Evershed flows associated with the more inclined and weaker fields of the penumbra. I will also identify discrepancies between our observational understanding of the penumbra and current sunspot models. The existence of serious points of disagreement calls for refined numerical simulations of sunspot structure.
Session: Sunspot Structure and Dynamics
Authors: A. Bemporad, G. Del Zanna, V. Andretta, M. Magri, G. Poletto, Y.-K. Ko
Title: An erupting filament and associated CME observed by Hinode, STEREO and SOHO
Abstract: A multi-spacecraft campaign was set up in May 2007 to observe the off-limb corona with Hinode, STEREO and SOHO instruments (Hinode HOP 7). During this campaign, a filament eruption and a coronal mass ejection (CME) occurred on May 9 from NOAA 10953 at the West limb. The filament eruption starts around 13:30 UT and results in a CME at 4°SW latitude. Remarkably, the event was observed by STEREO (EUVI and COR1) and by the Hinode/EIS and SOHO/UVCS spectrometers. We present results from all these instruments. High-cadence data from Stereo/EUVI A and B in the HeII 304 A line were used to study the 3-D expansion of the filament. A slow rising phase, during which the filament moved southward, was followed by an impulsive phase during which the filament appeared to change direction and then contribute to the westward-expanding CME as seen in STEREO/COR 1. Hinode/EIS was scanning with the 2" slit the region where the filament erupted. The EIS spectra show remarkable non-thermal broadening in lines emitted at different temperatures, in the location of the filament eruption. The CME was also observed by the SOHO/UVCS instrument: the spectrograph slit was centered at 1.7 solar radii, at a latitude of 5°SW and recorded a sudden increase in the O VI 1032-1037 A and Si XII 520 A spectral line intensities. We discuss the overall morphology of this interesting eruptive event, and provide a preliminary assessment of its temperature and density structure.
Session: Source of the Solar Wind/CME
Authors: Svetlana Berdyugina, Mägli, S., Fluri, D., Afram, N., Lites, B.
Title: 3D structure of the sunspot umbra
Abstract: We present an analysis of Hinode spectropolarimetric data of a large sunspot with a cold umbra. We applied an inversion technique to the data recorded in the 6302 A region including two Fe I lines and many TiO and CaH molecular lines. The inversions reveal a 3D structure of the dark nucleus, umbral dots, light bridge and a diffuse background in the umbra.
Session: Sunspot Structure and Dynamics
Authors: T. E. Berger, T. J. Okamoto, T. Magara, A. M. Title, T. D. Tarbell, S. Tsuneta. G. de Toma
Title: New Findings on Prominence Dynamics (Invited Talk)
Abstract: We review the Hinode/SOT observations of prominences to date with emphasis on the discoveries of several new dynamic properties including Alfven wave propagation in active region prominences, plume upflows, and bubble instabilities in quiescent prominences. In addition we note that while all active region prominences in the database exhibit horizontal thread structuring, quiescent prominences are primarily vertically structured leading to the suggestion that the magnetic topology of these two types of prominences may be fundamentally different. We compare this finding to recent models of prominence magnetic structure. We also compare the dynamics seen in Hinode/SOT prominences with recent discoveries in MLSO H-alpha movies that may show similar phenomena.
Session: Solar Magnetic Activity
Authors: R. Bhattacharyya, B. C. Low and P. Smolarkiewicz
Title: Magnetic relaxation in an incompressible viscous fluid
Abstract: We demonstrate spontaneous current sheet formation during the relaxation of a three dimensional magnetic field in a viscous, perfectly conducting incompressible magnetofluid. The current sheet manifests itself in the form of magnetic tangential discontinuity created when different parts of the fluid press each other as it relaxes to the lowest magnetic energy state. One novel feature of the numerical scheme used for this purpose is the description of the magnetic field in terms of evolving flux surfaces which are possible sites of tangential discontinuity formation. The computation follows initial global flux surfaces of simple geometry as they evolve in time to more complex forms creating magnetic tangential discontinuities in the process. This work illustrates the physics of spontaneous current sheet formation as described in the Parker theory.
Session: Flare Physics
Author: : Laura Bone
Title: Interaction and Eruption of Active Region and Quiescent Filaments in association with the Flare and CME of 19th May, 2007.
Abstract: A CME which erupted on 19th May, 2007 was accompanied by a B9.5 flare and resulted in a magnetic cloud near Earth that was registered by the STEREO-B and WIND spacecraft on 22nd May. Two independent filaments, Active Region and Quiescent, are observed in the days before the flare and eruption. Observations of the filament merger and accompanying heating are presented. Dynamic behaviour of the filament during the merger is examined. This includes heating cycles, when filament material disappears from the H alpha images and is observed in emission by XRT, that precede a final filament disappearance, heating and eruption. These stages are observed by instruments on Hinode, STEREO and TRACE. The associated B 9.5 flare, whose formation is part of the eruption, has an extreme thermal character. Possible models for the merger topology and eruption instability are discussed.
Session: Source of the Solar Wind/CME
Author: Juan Manuel Borrero
Title: Are there field-free gaps near tau=1 in sunspot penumbrae?
Abstract:
The vertical stratification of the magnetic field strength in sunspot penumbrae is investigated by means of spectropolarimetric observations at high spatial resolution from the Hinode spacecraft. We find that, in those regions where the magnetic field is more inclined and the Evershed flow is strongest (penumbral intraspines), the magnetic field can either increase or decrease with depth. A more careful analysis suggests that the magnetic field initially decreases from logtau_5 = -3 until logtau_5 = -0.7, but increases again below that. These results make it highly unlikely that regions void of magnetic fields are present at, or right below, the tau_5=1 level in the penumbra. However, they are compatible with the presence of a horizontal flux-tube-like field embedded in a magnetic atmosphere.
Session: Sunspot Structure and Dynamics
Authors: J. Buechner
Title: From DC current heating to 3D reconnection - the modes of magnetic energy conversion in the chromosphere and corona investigated by means of numerical RMHD simulations based on Hinode observations
Abstract: With its high resolution observations Hinode provides unique new opportunities to enhance our understanding of the magnetic coupling between the photosphere and the corona via the chromosphere. The non-local and non-linear character of this coupling as well as the lack of direct observations of magnetic fields in chromosphere and corona makes it necessary to use numerical simulation methods to describe the main properties of the coupling processes. Appropriate models have to take into account the complex structure of the coronal magnetic field in its relation to its photospheric sources, the inhomogeneity of the strongly structured plasma, the coupling of ions to the neutral atoms in the chromosphere and the transition between different plasma regimes in the atmosphere of the Sun. We have developed a numerical modelling approach which takes these factors into account. Our model starts with the observed photospheric magnetic field and derives the consequences of the photospheric energy input. We applied our model to heating events in the quiet solar atmosphere, observed by Hinode. We found that due to the changing plasma conditions a transition takes place between DC current heating in the lower corona to 3D magnetic reconnection in higher layers.
Session: Bringing Modeling and Obvservations Together
Authors: : Mats Carlsson, Boris Gudiksen, Viggo H. Hansteen
Title: Dynamic MHD Models of the Chromosphere and Corona (Invited Talk)
Abstract: The question of what heats the solar corona has been one of the central problems in solar physics for more than fifty years. The non-radiative flux that powers the corona has to pass through the solar chromosphere, a region where all but a few percent of the flux is converted into heat and radiation. From increasingly detailed observations it is clear that this interface between the photosphere and corona is a very complex and dynamic region and that interpretation of the observations will give vital clues to the nature of the non-radiative flux.
It is now computationally possible to treat the full convection zone-photosphere-chromosphere-corona system with some degree of physical realism. We will describe recent results of such dynamic MHD models of the solar chromosphere and corona with special emphasis on using these models to interpret high resolution observations.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: : Rebecca Centeno
Title: Hinode's SP and Gband co-alignment
Abstract: We analyze the co-alignment between Hinode's BFI-Gband images and simultaneous SP maps with the aim of characterizing the general off-sets between them and the second order non-linear effects in SP's slit scanning mechanism. We provide calibration functions and parameters to correct for the nominal pixel scales and positioning.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: : Jongchul Chae
Title: Magnetic Activity on the Sun Revealed by Hinode/SOT (Keynote Talk)
Abstract: Hinode observations have given us an unprecedented opportunity of understanding fine-scale magnetic activities on the Sun. The data produced by the Solar Optical Telescope(SOT) are particularly useful in the investigation of the interaction between magnetic field and plasma in the photosphere and chromosphere, opening the new era of observational magnetohydrodynamics (MHD). As an illustration, I would like to introduce new results and questions in three topics we have worked on. One is the determination of scale-dependent magnetic diffusivity in the photosphere, which seems to be closely related to the turbulent cascade of magnetoconvection. Another topic is the nature of magnetic reconnection in the chromosphere as manifest in the flux cancellation observed in the photosphere. Our new result is that the rates of flux cancellation determined from Hinode/SOT are much higher than those determined from SOHO/MDI. I will discuss the physical implications of this finding. Finally, I will present our finding of a pattern of horizontal flows in a quiescent prominence that consisted of a number of vertical threads. We think that this flow pattern has an important clue to solving the mystery of vertical threads and downflows along the threads in quiescent prominences.
Session: Solar Magnetic Activity
Authors: : L. Yelles Chaouche, S. Solanki, M. Cheung, A. Lagg and M. Schussler
Title: Flux emergence at the solar photosphere
Abstract: We investigate the observational signature of flux emergence in the solar photosphere obtained with 3D radiation-MHD simulations. The simulations consider the emergence of a twisted magnetic flux tube through the solar surface. We study different stages in the emergence process, starting from the early appearance of the flux tube at the solar surface. At every stage we numerically compute Stokes profiles for the two iron lines Fe I 6301.5 {\AA} and 6302.5 {\AA}. We degrade the obtained profiles in spectral and spatial dimensions to simulate observation conditions. Then, following observational practice, we apply Milne-Eddington-type inversions to the synthetic spectra in order to retrieve different atmospheric parameters. The so obtained parameters are compared with observational results obtained with Hinode's SP by Okamoto et al. 2008. We find that both observations and simulations agree on the general picture of an upwardly emerging horizontal flux tube with sub-kilogauss field strength. The simulations show that after interaction with granulations, the field is redistributed to a more vertical configuration. During this process the initially upwardly emerging flux tube, slows down and the magnetized plasma concentrates in intergranular lanes with downflowing motion. The analysis of the magnetic filed vector indicates that the magnetic flux tube was less twisted in the observations comparing to simulations.
Session: Bringing Modeling and Obvservations Together
Authors: Mark Cheung, Manfred Schuessler, Ted Tarbell, and Alan Title
Title: Solar surface emerging flux regions: a comparative study of radiative MHD modeling and Hinode SOT obserations
Abstract: We present results from numerical modeling of emerging flux regions on the solar surface. The modeling was carried out by means of 3D radiative MHD simulations of the rise of buoyant magnetic flux tubes through the convection zone and into the photosphere. Due to the strong stratification of the convection zone, the rise results in a lateral expansion of the tube into a magnetic sheet, which acts as a reservoir for small-scale flux emergence events at the scale of granulation. The interaction of the convective downflows and the rising magnetic flux undulates it to form serpentine field lines emerging into the photosphere. Observational characteristics including the pattern of emerging flux regions, the cancellation of surface flux and associated high speed downflows, the convective intensification of photospheric flux tubes, the appearance of anomalous darkenings, the formation of bright points and the possible existence of transient kilogauss horizontal fields are discussed in the context of new observations from the Hinode Solar Optical Telescope. Implications for the local helioseismology of emerging flux regions are also presented.
Session: Bringing Modeling and Obvservations Together
Authors: S. Christe, S. Krucker, and H. Hudson
Title: The Microflare Height Distribution from RHESSI
Abstract: We report on the height distribution of soft and hard X-rays from large numbers (of order 104) of microflares observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) over five years of data beginning in 2002. These events invariably occur in active regions. The excellent spectral spectral resolution of RHESSI lets us clearly distinguish the thermal (~3-10 keV) from the nonthermal (~10-20 keV) sources. The statistical analysis is similar to that of Matsushita et al. (1992) for early observations from Yohkoh. We observe the expected limb-brightening pattern of occurrence towards the limb, leading to a peak that is about 0.01 solar radii above the limb. We fit this distribution with parametrized Monte Carlo models and with simple geometrical models and report the implications for active-region structure.
Session: Flare Physics Heating
Author: : Len Culhane
Title: The Unusual Thermal Flare of 19 May 2007 – Evidence for Direct Heating in the Corona?
Abstract: Observations with Hinode EIS and XRT, RHESSI and TRACE show that the GOES B9.5 class flare had a long-lived thermal hard X-ray source with little or no evidence of impulsive behaviour in hard X-ray or radio emission. EIS in particular observed the flare plasma in some 21 spectral windows that included emission lines from He II (Log T = 4.7) to Fe XXIV (Log T = 7.2). We present observations of a range of plasma upflow velocities and non-thermal line broadening from the emission lines. The RHESSI images and spectra suggest that heating due to energetic electrons is largely absent. We examine other possible heating mechanisms that could explain the presence of plasma at temperatures ranging up to 20 MK.
Session: Flare Physics
Authors: Sanja Danilovic
Title: Investigating the origin of high speed downflows in solar magnetic features
Abstract: Hinode/SP data reveal the frequent occurrence of high speed downflows in magnetic features located in the quiet Sun. Such high-speed downflows are also seen in 3D radiation MHD simulations that, when reduced to Hinode resolution, look quite similar to the observed ones. We study the 3D structure and the evolution of the magnetic field in the 3D simulations in search of the source of these rapid downflows.
Session: Bringing Modeling and Obvservations Together
Authors: Alisdair Davey, Jonathan Cirtain, Eva Robrecht
Title: Observations of an XRT jet driving a filament eruption.
Abstract: We explore an XRT jet and a subsequent unwinding filament eruption using data from XRT, EIS and a suite of solar instruments. We surmise that the reconnection in the XRT jet leads to both material being injected into the solar wind, and down-flowing material that precipitates a filament destabilization and subsequent eruption, creating, in effect, a mini-CME. We examine the characteristics of the CME produced and compare it to other small scale CMEs.
Session: Source of the Solar Wind/CME
Authors: C.E. DeForest & D.A. Lamb
Title: Does NFI resolve the fundamental scale of flux emergence in the solar network?
Abstract: Magnetic feature tracking of MDI data has revealed that the solar network is not formed primarily by emergence events at the few-arcsecond scale; rather, most network-scale network flux concentrations appear to be formed by coalescence of many smaller elements at the subgranular scale. Comparison between simultaneous data sets from SOHO/MDI and Hinode/NFI confirms this statistical result.
We report on a similar statistical analysis of the NFI data, to determine whether NFI resolves the fundamental scale of flux emergence. Image deconvolution using the measured PSF of NFI is required to measure evolution on these smallest scales.
Session: Solar Magnetic Activity
Authors: C.E. DeForest, L. Rachmeler, & C. C. Kankelborg
Title: Fluxon modeling of solar eruptive events
Abstract: The fluxon approach to MHD modeling was developed to study the interplay of topology, reconnection, and eruptive destabilization in a controlled environment where reconnection can be controlled explicitly. Our code, FLUX, is currently the only code that can perform controlled numerical experiments on the metastable systems that give rise to CMEs, jets, and other eruptive events; it also uses under 1% as much computing power as more conventional codes. An initial result is that the Aly-Sturrock criterion may be irrelevant to real solar features. We report on recent results, the status of the code, and incorporation of photopheric magnetograms to drive semi-empirical simulations.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Saar, S., DeLuca, E.E., Farid, S.
Title: Full Sun DEM's
Abstract: We use sets of full sun multi-filter observations to study the thermal structure of different solar features. The data sets include both full resolution and 8x8 binned observations with 8 or more filter combinations. We will present DEM profiles for QS, XBP, CH and AR. The existence of high temperature plasma in the QS will be investigated.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Authors: Farid, S., Saar, S., DeLuca E.E.
Title: Spatial, and Thermal Properties of X-Ray Bright Points
Abstract: Multi-filter full sun XRT observations are used to explore the spatial and thermal prosperities of bright points identified by an automated XBP finder. There is a tendency of XBP to be hotter with increasing size. We have also found a class of XBPs that are particularly hot.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Author: : G. Del Zanna and S. Bradshaw
Title: Coronal loops: new insights from EIS observations.
Abstract: Multi-instrument observations of coronal loops of different active regions are presented. Hinode/EIS high-cadence observations clearly show how dynamic loops are at all temperatures. This clearly reflect the fast changes in the photospheric magnetic fields measured by SOT over a minute timescale. Despite that, persistent patterns are present. In particular, I will show that the pattern of dopplershifts and non-thermal widths in the TR-coronal lines, found for the first time in NOAA 10926 (cf. Del Zanna 2007, 2008), is actually a common feature in all active regions. This suggests that the majority of 'cool' (0.5-1 MK) loops are observed during their radiatively cooling phase. I will also discuss the complexities in measuring temperatures, densities and filling factors from the EIS spectra. Finally, I briefly discuss new atomic calculations and line identifications relevant for EIS.
Session: Perspectives on the Physics of Coronal Loops
Author: : G. Del Zanna V. Andretta, G. Poletto, Y.-K. Ko, L. Teriaca, and H. Mason
Title: Multi-instrument campaigns to observe the off-limb corona.
Abstract: Previous experience in organising multi-wavelength campaigns has clearly shown how important they are for science, despite the complexities and effort that goes into organising them. I briefly describe two campaigns I coordinated to observe the off-limb corona in 2007, and preliminary results obtained from them.
The first was a SOHO/Hinode/TRACE/STEREO/Ulysses week-long campaign during the SOHO-Ulysses quadrature in May 2007. The original aim was to measure Ne,Te, chemical abundances from the limb up to 1.7 solar radii, focussing on SOHO/CDS, Hinode/EIS, SOHO/UVCS. Various constraints somewhat limited our goal, however we were very fortunate in that an active region appeared on the Sun at the right longitude, and that a CME was observed by all instruments. The second one was a SOHO/Hinode/TRACE campaign to study the north polar coronal hole and measure the physical parameters of plume/interplume regions from the low corona to 1.7 solar radii, during the period 30 October - 4 November 2007. We obtained SOHO/CDS, SOHO/UVCS, TRACE, STEREO and Hinode observations, and during the SOHO/SUMER campaign a 1.5 days of targeted observations.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: : B. De Pontieu, M. Carlsson, S. McIntosh, V. Hansteen, T. Tarbell, L. Heggland
Title: Connecting Spicules and Alfven Waves in the Chromosphere (Invited Talk)
Abstract: In the past few years, high-resolution observations with ground-based telescopes and the Broadband Filter Imager (BFI) and Narrowband Filter Imager (NFI) of the Solar Optical Telescope onboard Hinode, as well as advanced radiative MHD numerical simulations have revolutionized our view of spicules and their role in the chromosphere. We review some of these results, including the discovery of two different types of spicules with different dynamics and formation mechanisms, as well as the finding that the chromosphere is riddled with strong Alfvenic waves. We further focus on the thermal evolution and velocities of spicules by comparing Dopplergrams made in the Na D 589.6 nm, H-alpha 656.3 nm and Mg B 517.3 nm passbands and filtergrams in the Ca H 396.8 nm passband, with SUMER UV spectra from transition region lines.
This work was supported by NASA contract NNM07AA01C. The Hinode mission is operated by ISAS/JAXA, NAOJ, NASA, STFC, ESA and NSC.
Session:Hinode Perspectives on Coronal/Chromospheric Heating
Author: : Kenneth Dere
Title: The plasma filling factor of coronal bright points
Abstract: Rastered spectra of regions of the quiet Sun were recorded by the Extreme ultraviolet Imaging Spectrometer during operations with the Hinode satellite. Calibrated intensities of Fe XII lines were obtained and images of the quiet corona were constructed. From the imaged spectra, the emission measures and geometrical widths of coronal bright points were obtained. From density-sensitive line ratios, electron densities were determined. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma-filling factor. The median electron density of coronal bright points is 4 $\times$ 10$^{9}$ cm$^{-3}$ at a temperature of 1.6 $\times$ 10$^6$K. The volumetric plasma filling factor of coronal bright points was found to vary from 4 $\times$ 10$^{-5}$ to 0.2 with a median value of 0.015.
Session: Perspectives on the Physics of Coronal Loops
Authors: DeRosa, Marc L. & Schrijver, Carolus J. & Barnes, Graham & Leka, K.D. & Lites, Bruce W. & Aschwanden, Markus J. & Thalmann, Julia & Valori, Gherardo & Wheatland, Michael S. & Wiegelmann, Thomas & Cheung, Mark & Conlon, Paul A. & Fuhrmann, Marcel & Inhester, Bernd & Régnier, Stéphane & Tadesse, Tilaye
Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar Corona: A Critical Assessment
Abstract: Nonlinear force-free field (NLFFF) modeling promises to provide accurate representations of the structure of the magnetic field above active regions, from which estimates of physical quantities of interest (e.g., free energy and helicity) can be made. However, the suite of NLFFF algorithms have so far failed to arrive at consistent solutions when applied to cases using the highest-available-resolution vector magnetogram data from Hinode/SOT-SP. It is our view that the lack of robust results indicates an endemic problem with the NLFFF modeling process, and that this process will likely continue to fail until (1) more of the far-reaching, current-carrying connections are within the observational field of view, (2) the solution algorithms incorporate the measurement uncertainties in the vector magnetogram data, and/or (3) a better way is found to account for the Lorentz forces within the layer between the photosphere and coronal base. In light of these issues, we conclude that it remains difficult to derive useful and significant estimates of physical quantities from NLFFF models.
Session: Bringing Modeling and Obvservations Together
Authors: G. de Toma, R. Casini, A.G. de Wijn, J.T. Burkepile, B.C. Low, K.S. Balasubramaniam, & T.E. Berger
Title: Observations of Large-Scale Dynamic Bubbles in Prominences
Abstract: Prominences are very dynamic, showing continuous motions down to their smallest resolvable spatial and temporal scales. However, as macroscopic magnetic structures, they are remarkably stable during their so-called quiescent phase. We compare recent ground-based and HINODE observations of large-scalebubble-like, dynamic substructures that form within quiescent prominences and rise through the prominences without disrupting them. We discuss the implications of these new observations for hydromagnetic models of prominences.
Session: Solar Magnetic Activity
Authors: Alfred de Wijn and Daniel Müller
Title: On the relationship between magnetic field and mesogranulation
Abstract: We investigate the relation between Trees of Fragmenting Granules (TFGs; Roudier et al. 2003) and the locations of concentrated magnetic flux in internetwork areas. The former have previously been identified with mesogranulation (Roudier & Muller, 2004). While a relationship has been suggested to exist between these features (e.g., De Wijn et al. 2005, Lites et al. 2008), no direct evidence has yet been provided.
Session: Solar Magnetic Activity
Authors: Alfred de Wijn, Scott McIntosh, Bart De Pontieu
Title: Interactions between reversed granulation, p-modes, and low-lying loops
Abstract: We investigate features that are observed in Ca II H sequences from Hinode in places where reveresed granulation seems to interact with p-modes. These features appear ubiquitously in the quiet sun. They are co-spatial with reversed granulation, and display similar general properties, but have sharper edges and show fast brightness change. They also appear predominantly above wide intergranular lanes, indicating a potential connection with low-lying magnetic loops. We report on the appearence and dynamics of these features using high-resolution, high-cadence observations from Hinode, and we discuss the possible implications of p-mode interactions with low-lying magnetic loops in the chromosphere.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: : T. Van Doorsselaere, V. M. Nakariakov, E. Verwichte, P. R. Young
Title: Waves in the solar corona: mode identification and using EIS to do seismological magnetic field measurements.
Abstract: Last year, Tomczyk et al. (2007) have conclusively proven that low amplitude (1km/s) waves are ubiquitously present in the corona. Using MHD wave theory, we demonstrate that fast magneto-acoustic kink waves reproduce the observational signatures reported by Tomczyk et al. (2007). We point out that Alfven modes take a torsional character and produce a spectral line broadening rather than a Doppler shift.
We present the results of numerical simulations of transverse velocity waves. These simulations show that the wave energy can only propagate along the magnetic field if perpendicular plasma structuring is present. As such, the discovery of low amplitude waves in the corona guided by the magnetic field constitute the seismological evidence that the corona has perpendicular density structuring.
We report the first spectroscopic detection of a kink MHD oscillation of a solar coronal structure by EIS. The detected oscillation has an amplitude of 1km/s in the Doppler shift of the FeXII 195Å spectral line (1.3MK), and a period of 296s. The unique combination of EIS's spectroscopic and imaging abilities enables us to measure simultaneously the mass density and length of the oscillating loop. This enables us to measure directly the magnitude of the local magnetic field, the fundamental coronal plasma parameter, as 39 \pm 8G, with unprecedented accuracy.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: : Frantisek Farnik
Title: The Soft X-ray Spectrophotometer SphinX for the CORONAS-Photon Mission
Abstract: At the end of this year a new solar satellite (CORONAS-Photon) will be launched in Russia. Among the scientific payload there will be the Polish instrument SphinX developed during the project of the Polish-Russian-Czech-Italian cooperation. The instrument will observe the soft X-ray spectra with high sensitivity and moderate spectral resolution. The poster describes the instrument characteristics, its calibration, precision and measurement philosophy. The scientific objectives are also given in details.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: C.E. Fischer, Alfred de Wijn, Rebecca-Centeno Elliott, Bruce Lites, C.U.Keller
Title: Analysis of high cadence HINODE SP quiet sun time series
Abstract: The HINODE SOT Spectro-polarimeter instrument can take full Stokes profiles with a high spatial and temporal resolution. This makes it possible to observe theoretically predicted mechanisms such as convective forcing and convective collapse. Filtergrams taken simultaneously in chromospheric lines give us the oppurtunity to relate the photospheric events with chromospheric behaviour of the magnetic elements. We present here a study of several time series taken with the HINODE SOT instrument.The data was recorded with the broadband filter in Ca II H, the narrowband filter in Mg I b and with the Spectro-polarimeter (SP) in dynamics mode. Thanks to the short exposure of the SP (1.6 sec) and the small field of view (30 slit positions) we can study events with a time development in the order of a minute. We identify and make a statistical analysis of events which are for example driven by convective forcing or show convective collapse.
Session: Solar Magnetic Activity
Authors: Th. Straus, B. Fleck, S.M. Jefferies, G. Cauzzi, S.W. McIntosh, K. Reardon, G. Severino, M. Steffen, T.D. Tarbell
Title: On the Role of Acoustic-gravity Waves in the Energetics of the Solar Atmosphere
Abstract: We revisit the dynamics and energetics of the solar atmosphere, using a combination of high-quality observations and 3D numerical simulations of the overshoot region of compressible convection into the stable photosphere. We discuss the contribution of acoustic-gravity waves to the energy balance of the photosphere and low chromosphere. We demonstrate the presence of propagating internal gravity waves at low frequencies (< 5mHz). Surprisingly, these waves are found to be the dominant phenomenon in the quiet middle/upper photosphere and to transport a significant amount of mechanical energy into the atmosphere outweighing the contribution of high-frequency (> 5mHz) acoustic waves by more than an order of magnitude. We compare the properties of high-frequency waves in the simulations with results of recent high cadence, high resolution Doppler velocity measurements obtained with SOT/SP and SOT/NFI on Hinode. Our results seem to be in conflict with the simple picture of upward propagating sound waves. We discuss the implications of our findings on the energy flux estimate at high-frequencies.
Session: Bringing Modeling and Obvservations Together
Authors: : Morten Franz, Rolf Schlichenmaier
Title: Spectral Analysis of Sunspot Penumbrae Observed with HINODE
Abstract: The nature of the energy transport in the penumbrae of sunspots is a controversially discussed aspect at the moment. Is it convection in magnetic field free gaps that exist in the space separating areas of strong magnetic field which is more or less static? Is it a convective flow that is channeled by magnetic flux tubes? Or is it by means of dissipative turbulent magneto-convection?
To investigate the plasma flow on a small scale we used spectropolarimetric data of sunspots at different heliocentric angles recorded by HINODE. We created maps of apparent Doppler velocities by taking advantage of the line shift of Fe 630.15 nm with respect to an averaged Fe 630.15 line core of the quiet Sun. Since we deduced the line shifts in the wing of Fe 630.15, that is, between 85 % and 95 % continuum intensity, we were able to visualize the flow pattern in the low photosphere.
In sunspot penumbrae close to disk center, the flow pattern along the line of sight, which we interpret as the vertical component of the Evershed flow, consists of a series of elongated ‘pearl chain’ like structures, extending radially through the entire center side penumbra. The up-flow appears not as a single elongated filament, but is concentrated in patches of strong up-flow separated by weaker up-flow or even down-flow. Due to projection effects the down-flow appears stronger on the limb side penumbra, but it is dislocated and spread out over a wide area in the outer penumbra. For sunspot penumbrae at large heliocentric angles these patterns are obscured by a combination of the horizontal Evershed flow and projection effects, but they are still ascertainable.
Session: Sunspot Structure and Dynamics
Authors: : Daisuke Fujimura, Saku Tsuneta
Title: Discovery of Alfven waves in the photosphere
Abstract: We present a discovery of propagating Alfven waves in the solar photosphere. We detect clear magnetic field and velocity fluctuations with amplitude of 50(G) (3.4%) and 0.17(km/s) (38%) respectively in vertical flux tubes with the@spectro-polarimeter of the Solar Optical Telescope (SOT) aboard Hinode satellite. Applying fast Fourier transform to the time profile of magnetic field strength and velocity, we found common strong peaks with period of 4-13 minutes, depending on flux tubes. We confirmed that these fluctuations are superposition of ascending and descending Alfven waves from the analysis@of the phase relationship between magnetic field strength and velocity. In@the case that ascending Alfven wave is stronger, Alfven velocity and density@at photosphere are estimated to be 4.9(km/s) and 9.0x 1017 (cm-3),@respectively, and the pointing flux is estimated to be 6.2x107@(erg/s/cm2).
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Dali Georgobiani, Junwei Zhao, Alexander Kosovichev, David Benson, Robert Stein, Ake Nordlund
Title: Applying helioseismic techniques to realistic simulations of solar convection
Abstract: We apply various helioseismic methods, as well as local correlation tracking, to realistic large scale simulations of solar convection, and compare some of the results to the SOHO/MDI high resolution observations and to the Hinode data. Our goal is to investigate the surface and sub-surface structures and test helioseismic measurements.We calculate the k-omega and the time-distance diagrams for the simulated data and show that the results are consistent with the SOHO/MDI observations. We apply the f-mode analysis to the simulated data, calculating travel time maps for surface gravity waves; travel time differences are proportional to the horizontal flow divergence. Calculating east-west and north-south travel time differences, we obtain proxies for the horizontal velocity components.We also apply correlation tracking technique to the simulated vertical velocity and calculate horizontal velocities. We compare these results to the actual simulated velocities. Both techniques successfully recover the flow pattern of the surface velocity field. All these methods reveal similar large scale convective patterns and provide a solid initial test of helioseismic techniques.
Session: Local Helioseismology with Hinode
Authors: M. K. Georgoulis, V. S. Titov, & Z. Mikic
Title: Current-Carrying Magnetic Flux Tubes in the Solar Atmosphere: Commonplace or a Rare Occurrence?
Abstract: We attempt a fresh look on the long-standing problem of neutralized vs. non-neutralized electric current patterns in solar active regions. A rather prevailing viewpoint being that active regions include significant non-neutralized electric currents but they are current-neutralized as a whole, many original studies had suggested revisiting the problem when data of higher resolution and quality were available. We calculate the electric current patterns using two vector magnetograms from Hinode's SpectroPolarimeter; one of an eruptive, and one of a non-eruptive, active region. We find that magnetic flux emergence does not simply inject raw electric currents in the solar atmosphere. Significant non-neutralized currents tend to flow only along strong magnetic polarity inversion lines (PILs), which only exist in a small percentage of active regions. The more flux-massive a PIL, the stronger the non-neutralized currents it contains. Concluding, we attempt an interpretation of this finding.
Session: Solar Magnetic Activity
Authors: Sarah Gibson
Title: Whole Heliosphere Interval (Invited talk)
Abstract: The Whole Heliosphere Interval (WHI) is an international coordinated observing and modeling effort to characterize the three-dimensional interconnected solar-heliospheric-planetary system at solar minimum, using observations originating at the Sun during Carrington Rotation 2067: March 20 - April 16, 2008. WHI's science begins with the solar interior and extends through the heliosphere and interplanetary space out to the heliopause. WHI is a special campaign period of the International Heliophysical Year, and involves the participation of many observatories and researchers around the world. In this talk I will highlight WHI research to date, including interdisciplinary studies which trace the effects of solar structures (e.g., open/closed magnetic boundaries, fast/slow solar wind) through the heliosphere, and analyze the transport of energy (e.g., magnetic and radiative) from below the solar surface out to the Earth.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: : Green, L.M., Kliem, B., Toeroek, T., van Driel-Gesztelyi, L., Attrill, G.
Title: What can soft X-ray sigmoids tell us about flux rope formation and associated eruptions?
Abstract: Soft X-ray images of the Sun have shown that some active regions contain loops, or collections of loops, which appear forward or reverse 'S' in shape. These structures are known as sigmoids and are of interest because sigmoidal active regions have a high probability of producing an eruption.
Different models have been put forward to explain the magnetic topology of sigmoids. We investigate these models by studying filament eruptions from sigmoid regions. In several cases we find a clear sign of rotation of the filament apex as it erupts which indicates a conversion of twist to writhe in a flux rope topology during this phase. However, the direction of rotation shows that the sigmoid is not contained in the flux rope. We use Hinode and Yohkoh observations to further investigate which sigmoid models are realistic and when and how the flux rope formation occurs. We find evidence for a transition from an arcade to a flux rope topology as well as evidence for a bald patch separatrix surface under a flux rope in some events.
Session: Bringing Modeling and Obvservations Together
Authors: : Paolo C. Grigis, Edward DeLuca, Leon Golub
Title: XRT observations of quiet Sun nanoflares
Abstract: We present high-cadence Hinode/XRT soft X-ray observations of the quiet Sun corona and a statistical analysis of its variability on short timescales (minutes to hours). Localized brightenings (nanoflares) are observed mostly in confined structures characterized by the presence of compact, bright, hot loops (bright points). Brighter structures are associated with stronger activity, suggesting that they are heated by the nanoflares. We explore the connection between this coronal activity (as mapped from the soft X-ray image sequences) and the underlying magnetic field structures.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Leon Golub, Alexander Engell, Adriaan A. van Ballegooijen, Kelly E. Korreck, and Katharine K. Reeves
Title: Modeling the Twisted Coronal Loops in AR 10938
Abstract: Hinode/XRT observations of AR 10938 on 2007 Jan 18 indicate that the coronal loops observed in this active region are not aligned with the potential field. Based on an MDI magnetogram, we construct a non-linear force-free field (NLFFF) model of the active region by injecting electric currents parallel to the potential field lines and evolving the field to a force-free state using magneto-frictional relaxation. The current distribution is adjusted such that selected model field lines fit the observed coronal loops. Although the fit is not unique, this provides an estimate of the 3D shape of the observed loops and magnetic field strength as function of position along the loops. Using this information, we construct models of temperature and density along these loops. The results are compared with XRT observations in different filters. This work is funded by the Hinode/XRT contract from NASA to SAO.
Session: Perspectives on the Physics of Coronal Loops
Author: : Mandy Hagenaar
Title: Magnetic Flux Emergence on Different Scales
Abstract: Magnetic flux emerges on the Sun on many different scales, from weak intranetwork to network concentrations and (ephemeral) active regions. Methods previously developed to recognize regions of magnetic emergence on MDI Full Disk magnetograms fail when applied to Hinode/SOT Stokes maps: the resolution is so much higher that simple bipoles on MDI are observed as collections of fragments. We present a new method for the automated detection and characterization of flux emergence on a range of scales, Our findings are compared with simulations, and we discuss the implications for our understanding of emerging flux ropes.
Session: Solar Magnetic Activity
Authors: : I. G. Hannah
Title: Combined RHESSI and Hinode Flare Observations (Invited Talk)
Abstract: Thousands of flares have been observed with RHESSI since Hinode launched in late 2006 and hundreds of these events have coverage with both spacecraft. The combination of these data sets provides powerful insights into the underlying flare physics of particle acceleration and heating. I will discuss the flare observations that have been done using both RHESSI and Hinode and possible future analysis.
Session: Flare Physics
Authors: E. P. Kontar and I. G. Hannah
Title: Regularized inversion techniques for the analysis of XRT Differential Emission Measures
Abstract: Hinode XRT provides unprecedented spatial resolution knowledge of the plasma temperature distribution resulting from heating in the solar atmosphere. However, the inference of the Differential Emission Measure DEM(T) from XRT raw data is an ill-posed inverse problem. Here, we develop and apply an enhanced regularization algorithm used in RHESSI X-ray software for this process making use of general constraints on the form of the differential emission measures. We show by simulations that this technique yields DEM(T) with considerably more information and higher quality than previous algorithms. The algorithm naturally provides signal dependent resolution of the method thus giving a clear criteria to determine whether the plasma is consistent with isothermal model.
Session: Flare Physics
Authors: : H. Hara
Title: Coronal Plasma Motions in Active Region Loops Observed with Hinode EIS
Abstract: The solar active region 10938 has been observed from the disk center to the west limb with the Hinode EUV Imaging Spectrometer. In the disk center observation, subsonic upflow motions of tens of km/s and enhanced nonthermal velocities have been found near the footpoints of the active-region loops assuming a single Gaussian approximation for the emission-line profiles. When the same part of the active region is observed near the limb, both upflows and enhanced nonthermal velocities essentially decrease. There is a strong correlation between Doppler velocity and nonthermal velocity. Significant deviations from a single Gaussian profile are found in the blue wing of the line profiles for the upflows. These suggest that there are unresolved high-speed upflows. We discuss the implications for coronal heating mechanisms.
Session: Perspectives on the Physics of Coronal Loops
Author: : Louise Harra
Title: Outflows related to flares and CMEs (Invited Talk)
Abstract: This invited review will concentrate on the latest results from Hinode regarding the response to the corona during an eruptive event. The changes in the atmosphere can be long lasting, and Hinode now allows us to observe the velocity structure in the atmosphere.
Session: Source of the Solar Wind/CME
Authors: L. Heggland, B. De Pontieu and V. H. Hansteen
Title: Observational signatures of simulated reconnection events in the solar chromosphere and transition region
Abstract: We present the results of numerical simulations of wave-induced magnetic reconnection in a model of the solar atmosphere from the photosphere to the corona. In the magnetic field geometry we study, the waves, driven by a monochromatic piston and a driver taken from Hinode observations, induce periodic reconnection of the magnetic field, and this reconnection appears to help drive long-period chromospheric jets. We produce simulated observations in several transition region and chromospheric lines, and find many similarities to the signatures of explosive events, some types of spicules and other phenomena thought to be caused by reconnection.
Session: Bringing Modeling and Obvservations Together
Authors: Hudson, H.S., Fivian, M.D., Zahid, H.J.
Title: Implications of RHESSI measurements of solar shape and faculae
Abstract: The solar aspect sensors of the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) allow us to study the precise shape of the Sun in a narrow bandpass filter at about 6700A. The measurement is analogous in some ways to Dicke's original oblateness measurements. Interpreted strictly as limb position, the individual measurements have a precision of a few milli arcsec (mas), and we have been obtaining about 100 points per second since launch in February 2002. We find the oblateness of the Sun (the difference of equatorial and polar radius) in July-September 2004 to have been 7.98+-0.14 mas, consistent with the expectation from the surface rotation rate. To obtain this result we made use of the (positive) correlation we observed between the RHESSI radius value and the brightness of the EIT 284A limb. This correlation establishes a relationship between facular brightening and apparent radius. On-disk data show that facular contrast has a maximum at intermediate values of mu and decreases again at the extreme limb. The behavior of the contrast at the extreme limb is not well understood at present, but the limb observation show that it cannot go exactly to zero. We discuss this in the context of the "hot wall" and cloud models of faculae and plage, noting that the hot wall model would predict zero contrast at the limb.
Session: Solar Magnetic Activity
Authors: Hui Tian
Title: Cool and hot components of a coronal bright point
Abstract: We performed a systematic study of the Doppler shifts and electron density measured in an EUV bright point observed simultaneously in more than 10 EUV lines with formation temperatures from log(T/K) = 4.5 to 6.3. Those parts of a BP seen in transition region and coronal lines are de¯ned as its cool and hot components, respectively. We find that the transition from cool to hot occurs at a temperature around log(T/K) = 5.6+-0.1. The two components of the BP reveal a totally different orientation and Doppler-shift pattern, which might result from a twist of the associated magnetic loop system. The analysis of magnetic-field evolution and topology seems to favour a two-stage heating process, in which magnetic cancelation and separator reconnection are powering, respectively, the cool and hot components of the BP. We also found that the electron densities of both the cool and hot components of the BP are higher than those of the surrounding quiet Sun, and comparable to or smaller than active-region densities.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Authors: Kiyoshi Ichimoto and SOT team
Title: Convective nature of the Evershed Effect Observed by SOT/Hinode
Abstract: The Evershed effect has been one of the longstanding mystery in solar physics in its nature and origin. The Solar Optical Telescope (SOT) aboard Hinode revealed the fine scale structure of the Evershed flow and its relation to the filamentary structures of the sunspot penumbra; The Evershed flow is confined in narrow channels with nearly horizontal magnetic fields embedded in deep layer of penumbral atmosphere. It is a dynamic phenomenon with the flow velocity close to the sound speed in the photosphere, and individual flow channels are associated with tiny upflow (source) at the inner end and down flow (sink) at the outer end. The penumbral bright grains are exactly correlated with the upflowing gas, thus the Evershed flow is certainly carrying the heat to maintain the penumbral brightness. SOT/Hinode also discovered the twisting appearance of penumbral filaments which may be attributed to the overturning convective motions. thus the Evershed effect may be naturally interpreted as a consequence of the convection under the strong inclined magnetic field in sunspot penumbra. We will discuss the current penumbral models, i.e., the rising flux tube model and the gappy model, in the lights of the new observations provided by Hinode.
Session: Sunspot Structure and Dynamics
Authors: Yusuke Iida, Takaaki Yokoyama and Kiyoshi Ichimoto
Title: The vector magnetic and Doppler velocity fields at the cancellation sites
Abstract: Spatial structures and time evolutions of the vector magnetic and Doppler velocity fields around the magnetic cancellatoin sites are studied by using the Hinode SOT Spectropolarimeter (SP) and Filtergrams (FG). Two senarios, i.e. the "U-loop emergence" and "Omega-loop submergence" scenarios are theoretically suggested, but it is still indefinite which of them occurs in the cancellation regions. In order to study this, the magnetic and velocity field structures at the cancellation sites are investigated. We used the data sets of the quiet sun to find relatively isolated cancellation events away from, e.g., plages or networks. Two cancellation events are studied in detail so far. >From the vector magnetic data synthesized from the SP observations, we found a horizontal field (100 - 300 Gauss) connecting the colliding opposite polarities in each of the investigated events. We also found stable red-shift downflow patches around the cancellation sites by using the Dopplergrams obtained by the FG at the NaI wavelength band. Note that the effect of the 5-minute oscillations was subtracted from the images by taking temporal averages over longer than five minutes. Interestingly, the red-shift patches are already seen in each of the positve and negative polarities even before the collision. They show an apparent motion toward the collision site during the cancellation event along with the appearance of the horizontal field. We interpret that these magnetic and velocity structures and evolutions support the submergence scenarios at the cancellation sites.
Session: Solar Magnetic Activity
Authors: S. Imada, H. Hara, T. Watanabe, A. Asai, T. Minoshima, L. K. Harra, and J. T. Mariska
Title: Non-Gaussian line profiles associated with flows in a large solar flare (Invited Talk)
Abstract: We studied the characteristics of the non-Gaussian line profile of Fe XIV in and around the flare arcade (13th Dec 2006). We found that the broad non-Gaussian line profiles associated with redshifts were observed in the flare arcade. There were two typical types of broad line profile. One was distorted line profile caused by multiple flows, and the other was symmetric line profile without any additional component. We successfully distinguished those two types by higher order statistical moments or M defined in this talk. The distorted/symmetric broad line profiles were preferentially observed in new/old flare loops, respectively. The symmetric broad line profiles can result from the turbulence. Our results may indicate that the old flare loops stores the turbulent plasma.
Session: Flare Physics
Authors: K. Ishibashi
Title: Plasma Temperature of Hot and Diffused Emission in the Quiet Sun Coronae
Abstract: High throughput and sensitivity of the Hinode/XRT allow us to detect hard X-ray plasma at much lower emissivity than the Yohkoh/SXT could. Through medium-Beryllium filter, the Hinode/XRT detected the presence of hard X-ray diffused coronal plasma (T ~ 5 -- 10MK) in the Quiet Sun state. The presence of such hot emission -- not related to any active regions -- appears to be somewhat restricted in the mid-latitude region in space, but somewhat ubiquitous in time.
A question has been raised as to whether the plasma temperatures of those diffused structures truly approach to ~10MK. With multi-filter observations by the Hinode/XRT, a crude spectroscopic analysis can be performed to identify if a copious amount of hot X-ray emission (e.g., Si XIII forming at kT ~ 0.86keV or other lines below 10AA) are present in their spectra. This presentation addresses results of such plasma diagnostics.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Ryohko Ishikawa and Saku Tsuneta
Title: Statistical properties of transient horizontal magnetic fields
Abstract: Following discovery of horizontal magnetic field with ASP (Lites et al 1996), and the SOLIS and GONG instruments (Harvey et al. 2007), high resolution spectro-polarimetric observations with the SOT have confirmed this finding, and extended the studies considerably (Lites et al 2008, Centeno et al. 2007, Orozco Suarez et al. 2007, Ishikawa et al. 2008, Ishikawa & Tsuneta 2008, Tsuneta et al. 2008).
We present statistical properties of the transient horizontal magnetic field (THMF). The topics to be reported include (1) size and life time distribution, (2) vertical speed of THMF, (3) locations of emergence and disappearance in terms of granular structure, (4) PDF (probability distribution function) of intrinsic magnetic field strength, filling factor, and degree of linear polarization (5) orientation of the field vector. The extensive statistical survey reveals numbers of so far unknown unique and remarkable properties of THMFs, leading us to conclude that 1) THMFs are receptive to convective motion and 2) a local dynamo processes is essentially responsible for THMFs. We also estimate the magnetic energy flux carried by THMFs based on the statistical data and find that these magnetic energy fluxes are comparable to total chromospheric and coronal energy loss (Withbroe & Noyes 1977), implying a role of THMF for chromospheric heating and dynamism (Ishikawa and Tsuneta 2008).
Session: Solar Magnetic Activity
Author: : Aase Marit Janse
Title: Spontaneous Current Sheets: Radically different in 3D fields vs in 2D fields
Abstract: We present mathematical models to demonstrate the inevitability of current-sheet formation in a magnetic field governed by the ideal hydromagnetic induction equation, as described by the Parker theory. This process, central to the heating of the solar corona, is radically different in fully three-dimensional fields as compared with two-dimensional fields. Magnetic neutral points or separatrix flux surfaces are necessary for sheet formation in two-dimensional fields. In fully three-dimensional fields, current sheets form readily even in the complete absence of neutral points and separatrix surfaces, and, these sheets can form densely throughout the field in response to changes in the magnetic volume. This general result is established for fields that are topologically untwisted, including the first direct demonstration of sheet formation in the absence of any magnetic neutral point. Implications of this basic result for understanding the flare phenomenon will be discussed.
Session: Flare Physics
Author: : Phil Judge
Title: New Perspectives on the Chromosphere/Transition Region" (Keynote Talk)
Abstract: I will review observations and theoretical work concerning the role of the chromosphere as the lower boundary for the corona. I will highlight the need for measurements of the chromospheric magnetic field as the plasma regimes change from beta $>$ 1 to $<$ 1, using a striking observational example. I will review some of the important physical processes occurring within the partially ionized chromosphere which can greatly alter the conditions at the coronal base from those expected based only upon photospheric measurements. I will re-iterate the obvious conclusion, but one often ignored, that one must understand specific chromospheric processes if one is to have hope of addressing the nature of the supply of mass, momentum and energy into the corona.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Suguru Kamio, Hirohisa Hara, Tetsuya Watanabe, and Werner Curdt
Title: Outflows from the Sun (Invited Talk)
Abstract: We studied properties of coronal jet and explosive events in a polar coronal hole and their relationship with photospheric magnetic fields. Hinode/SUMER collaboration allowed us to investigate small-scale activities in the coronal hole with a broad temperature coverage. Coronal jets are classified into two categories; transient jets and stable jets associated with bright points lasting over one hour. Detailed analysis indicates that their locations coincide with localized strong magnetic fields in the photosphere, which are perpendicular to the local surface. There are also cool upflows and explosive events only identified in transition region temperatures. They preferably occurred near weak network fields which may be low-lying fields in the transition region. We summarize properties of observed events and discuss their implications for the magnetic configuration in the coronal hole.
Session: Source of the Solar Wind/CME
Authors: Ryouhei Kano
Title: Photospheric Magnetic Activities to Trigger Micro-Flares observed with the Hinode SOT and XRT.
Abstract: For understanding the coronal heating, it is important to reveal the coupling between photospheric magnetic activities and coronal transient events. Micro-flares are a good target to study the coupling, because they are smaller and simpler than flares.
In the active region 10923, no major flare happened on November 14, 2006, but many micro-flares were observed with the Hinode X-ray Telescope (XRT). We used a set of longitudinal magnetogram taken with the filtergpam of the Hinode Solar Optical Telescope (SOT). We found that most of the micro-flares were associated with magnetic activities below their footpoints. From the observation, flux emergence is the dominant source to trigger micro-flares.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Authors: Kato, Y., Magara, T., and Shimizu, T.
Title: Radiation Transfer Analysis on Heating Mechanism of Magnetohydrodynamic Emerging Magnetic Flux Tubes
Abstract: In spite of the large number of magnetohydrodynamic (MHD) simulations of the emerging flux tube in the solar atmosphere, radiation properties of the MHD emerging flux tube have been poorly understood. This is because a heating at the footpoint of the emerging magnetic field lines is significant and the heating process accompanied with the heat conduction and the vaporation in the MHD flux tube have not been worked out yet. In this study, by using a heating model based on MHD data, we have performed three-dimensional (3-D) multi-wavelength radiation transfer calculation of the MHD emerging flux tube in order to examine our MHD models and also to identify a possible heating mechanism of the observed X-ray coronal loops. It is found that the current dissipation model are difficult for reproducing the structure of X-ray loops observed by Hinode XRT and Yohkoh SXT. This suggests that alternative modeling of heating process should be incorporated into our MHD models. We discuss some unresolved issues of heating process in the MHD emerging flux tube.
Session: Perspectives on the Physics of Coronal Loops
Authors: : Jun'ichi Kotoku(NAOJ), Toshifumi Shimizu(ISAS/JAXA), Ryousuke Imada(NAOJ), Yukio Katsukawa(NAOJ), Ryouhei Kano(NAOJ), Saku Tsuneta(NAOJ), Taro Sakao(ISAS/JAXA), Hinode team
Title: Long time observation of X-ray bright point with Hinode
Abstract: We observed quiet region for 13 hours on 10 Oct 2007 with Hinode and found X-ray bright points with magnetic canceling feature. This system consists of three magnetic poles: positive, negative, positive. West two poles showed clear magnetic cancelation feature. During the observation time, there seemed to be no strong correlation with X-ray light curve and the flux of magnetic fragments around footpoints. We report magnetic features and time evolutions of this X-ray bright point.
Session: Solar Magnetic Activity
Authors: : Y. Katsukawa, J. Jurcak, K. Ichimoto, Y. Suematsu, S. Tsuneta, T. Shimizu, T. E. Berger, R. A. Shine, T. D. Tarbell, B. W. Lites
Title: Chromospheric Activity at the Smallest Scales Obtained by Hinode (Invited Talk)
Abstract: HINODE Solar Optical Telescope (SOT) found ubiquitous occurrence of fine-scale jetlike elongated brightenings in penumbral chromospheres, which are referred to as penumbral microjets. Their very transient nature suggest that magnetic reconnection in interlaced magnetic field configuration is the most possible cause of penumbral microjets. In order to understand magnetic configuration driving penumbral microjets, we investigated relationship between penumbral microjets seen in CaII H images and photospheric magnetic fields measured by the SOT spectro-polarimeter. We found the inclination angles of penumbral microjets derived with CaII H images are roughly consistent with inclination angles of a relatively vertical background component in uncombed magnetic field configuration. In addition, we found small areas with downflows at photospheric layers that are coincident with brightenings seen in Ca II H images. The size of the downflow patches is 0.5'' or smaller. They are sporadically observed in the center-side penumbra and have different geometry from the Evershed flow. We derived, using a Stokes inversion technique with height-dependent atmospheric model, that the downflows preferentially take place in the lower photosphere. The downflow is a possible signature of the chromospheric brightenings in the penumbra and might correspond to downward outflows driven by magnetic reconnection.
Session: Solar Magnetic Activity
Authors: : R. KITAI, T. KAWATE, Y. HASHIMOTO, T. MATSUMOTO, H. WATANABE, K. OTSUJI, T. NAKAMURA, N. NISHIZUKA, K. NISHIDA, S. UENO, S. NAGATA AND K. SHIBATA
Title: Solar Plages : Chromospheric Heating and Spicular Mass Ejections
Abstract: At Hida observatory of Kyoto University, we continue to study the heating and mass ejection phenomena in the solar chromosphere with Domeless Solar Telescope (DST) and Solar Magnetic Activity Research Telescope (SMART). In this work, we will report some recent cooperative observational results with Hinode on the following topics:
(1) Plage heating and waves Analysis of a long time series of CaII K spectrograms at a plage area showed us a clear co-existence of 3- and 5-min oscillation in Doppler velocity. The phase relation between the Doppler velocity and the intensities of CaII K line showed different behavior according to the oscillatory mode. We simulated the response of the VAL model atmosphere to the input of 3-min or 5-min acoustic disturbances, in 1-D geometry. With the results of CaII K line profile synthesis by MULTI code of the disturbed atmosphere, we will discuss unsteady heating of plage chromosphere similar to the quiet chromospheric heating model proposed by Carlsson and Stein (1997).
(2) Disk spicules in and around plage regions After applying a special image processing (MADMAX) to SOT/Hinode BFI images in CaII H, we clearly identified numerous ejecting features in a plage area. Their morphological shapes of thin tapered cylinder and their dynamics strongly suggest us that they are spicules in a plage. The plage area was observed spectroscopically in Ca II H&K lines with the DST telescope, simultaneously as the SOT/Hinode BFI observation. Basic properties of these spicular features will be reported and be discussed from the view point of Type I, II classification of limb spicules ( de Pontieu et al. 2007).
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: I.N. Kitiashvili, L. Jacoutot, A.G. Kosovichev, N.N. Mansour, A.A. Wray
Title: Realistic Numerical Modeling of Solar Magnetoconvection and Oscillations
Abstract: We have developed 3D, compressible, non-linear radiative magnetohydrodynamics simulation to study the influence of the magnetic field of various strength and geometry on the turbulent convective cells and on the excitation mechanisms of the acoustic oscillations by calculating spectral properties of the convective motions and oscillations. The results reveal substantial changes of the granulation structure with increased magnetic field, and a frequency-dependent reduction in the oscillation power in a good agreement with Hinode observations. These simulations results explain the enhanced high-frequency acoustic emission observed at the boundaries of active region ("acoustic halo" phenomenon). This phenomenon is caused by the changes of the spatial-temporal spectrum of the turbulent convection in magnetic field, resulting in turbulent motions of smaller scales and higher frequencies than in quiet Sun regions. The results of the realistic simulations and comparison with the Hinode data provide important insight into the structure of the turbulent magnetoconvection, turbulent energy transport, and excitation mechanism of solar acoustic waves.
Session: Bringing Modeling and Obvservations Together
Authors: James A. Klimchuk
Title: Models of Coronal Loops (Keynote Talk)
Abstract: It is often said that coronal loops are the fundamental building blocks of the magnetically-closed corona. This is certainly true, especially when one realizes that the diffuse component of the corona can be thought of as a collection of indistinguishable loops. During the Skylab era, it was believed that loops are in states of quasi static equilibrium. However, more recent observations combined with numerical models have revealed that this interpretation is not correct, at least for many loops. The concept of loops as bundles of impulsively-heated strands is very appealing and solves many of the problems faced by static models, but it too faces observational challenges. Yet another idea involves the fascinating phenomenon of thermal nonequilibrium. I will review the various attempts to model coronal loops and discuss how they agree and disagree with observations, paying particular attention to the latest results from Hinode.
Session: Perspectives on the Physics of Coronal Loops
Authors: Yuan-Kuen Ko, George A. Doschek, Harry P. Warren
Title: Ultra-Hot Plasma in Active Regions Observed by the Extreme-ultraviolet Imaging Spectrometer on Hinode
Abstract: The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft obtains high resolution spectra of the solar atmosphere in two wavelength ranges: 170 - 210 and 250 - 290 angstroms. These wavelength regions contain a wealth of emission lines covering temperature regions from the chromosphere/transition region (e.g., He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII, Fe XXIV). Of particular interest for understanding coronal heating is a line of Ca XVII at 192.86 angstroms, formed near a temperature of 5 million degrees. This line is blended with lines of Fe XI and O V. However, by using a specific procedure outlined in this paper, the Ca XVII line can be extracted from the blended emission. EIS has obtained many raster observations of active regions by stepping the slit in small increments across the active region, producing monochromatic images of the active region. The Ca XVII blend has been included in many of these rasters. In this paper we discuss the procedure to extract the Ca XVII line from the blend and show examples of the 5 million degree plasma emission in several active regions. We find that the 5 million degree corona has two morphological features in these active region loops -- `fat' medium-sized loops confined in smaller regions than the 1-2 million degree corona, and diffusive emission surrounding these loops. We discuss the emission measure of the 5 million degree plasma relative to the cooler plasma in the active regions.
Session: Perspectives on the Physics of Coronal Loops
Authors: K. E. Korreck (1), G. Stenborg (2)
1. SAO 2. Interferometrics, Inc.
Title: Flows from Flaring Active Regions Observered with Hinode's XRT and STEREO
Abstract: Outflows from the Sun somehow make up the solar wind. The fast solar wind is now attributed to coronal holes, however, the source of the slow solar wind is more uncertain. Recent work has pointed to flow coming from the edges of active regions as the source of the slow solar wind. We explore outflows from Hinode's XRT as well as STEREO to understand the outflow parameters. The outflow information is used to propagate a solar wind parcel to 1AU. The ACE SWICS data is then used to compare outflows seen at these sources and then at 1AU.
Session: Source of the Solar Wind/CME
Authors: A.G. Kosovichev
Title: Recent Progress and Future Directions for Helioseismology (Invited Talk)
Abstract: Hinode/SOT observations provide unique data for high-resolution helioseismology. These data have allowed us for the first time to resolve the subsurface convective boundary layer, investigate the structure of sunspot oscillations, detect flare-generated MHD waves in the sunspot umbra, carry out multi-wavelength studies of solar oscillations, and obtain helioseismic data for probing the subsurface dynamics in near-polar regions. The future directions in helioseismology will be focused on understanding the mechanism of solar dynamo, diagnostics of emerging magnetic flux, formation and evolution of sunspot regions and their flaring activity. These tasks require development of new helioseismology methods for probing conditions in strong magnetic field regions and in the deep convection zone, including the tachocline. The new developments in helioseismology will be supported by realistic MHD simulations and based on massive data analysis from Hinode and Solar Dynamics Observatory.
Session:
Authors: Sam Krucker and R.P. Lin
Title: Coronal hard X-ray thin target bremsstrahlung emission from flare-accelerated electrons
Abstract: Coronal hard X-ray emissions provide unique information about the supra-thermal electrons closest to the site in the corona where their acceleration is believed to occur. However, the intense hard X-ray emissions from footpoints of flare loops generally make it impossible to observe faint coronal sources. Coronal hard X-ray emissions from flare-accelerated electrons are therefore best observed in partially-limb occulted flares.
Here we present X-ray observations of a partially limb-occulted solar flare taken by the X-ray telescope (XRT) onboard Hinode and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Non-thermal X-ray emission during the impulsive phase is observed to come from a coronal loop. Two minutes later at the soft X-ray peak, the non-thermal loop seen in the impulsive phase is observed in thermal soft X-ray emission. This support the standard flare model where flare-accelerated non-thermal electrons produce thin target hard X-ray emission in the flare loop and precipitate into the chromosphere heating and evaporating hot plasma that fill the flare loop. These observations provide one of the best evidence for hard X-ray thin target bremsstrahlung emission from flare-accelerated electrons in the corona.
Session: Flare Physics
Authors: : Masahito Kubo
Title: Magnetic Flux Loss and Flux Transport in a Decaying Active Region
Abstract: We estimate the temporal change of magnetic flux perpendicular to the solar surface in a decaying active region by using a time series of the spatial distribution of vector magnetic fields in the photosphere. The vector magnetic fields are derived from full spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux transport rate in a decaying sunspot and its surrounding moat region. The amount of magnetic flux that decreases in the sunspot and moat region is very similar to magnetic flux transported to the outer boundary of the moat region. The flux loss rates of magnetic elements with positive and negative polarities are balanced each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the outer boundary of the moat region.
Session: Sunspot Structure and Dynamics
Authors: Masahito Kubo
Title: Evolution of Vector Magnetic Fields of Dark-cored Penumbral Filaments
Abstract: We investigate temporal change of the vector magnetic field and velocity field in a dark-cored penumbral filament, using a time series of G-band images and simultaneous spectropolarimetric measurements with the Solar Optical Telescope aboard the Hinode spacecraft. Magnetic and velocity field maps with a 5.5 minute cadence are derived from the spectropolarimetric measurements with an assumption of a Milne-Eddington atmosphere. Strong Evershed flows are observed along the dark core and originate from a penumbral bright grain. The dark core having the strong Evershed flows elongates toward the umbra with the inward motion of the penumbral bright grain. The dark core has weaker and more horizontal fields than its lateral brightenings when the Evershed flows are observed. It is confirmed that Evershed flows are closely related to the formation of the weaker and more horizontal magnetic fields. The horizontal magnetic fields with the Evershed flows disappears at almost same time as the disappearance of the penumbral bright grain, but the dark core still survives for 10-20 minutes after that. During this period, the dark core gradually becomes as bright as its lateral brightenings. These results suggest that the dark core is formed by cooling of the plasma carried by the Evershed flows.
Session: Sunspot Structure and Dynamics
Authors: Andreas Lagg (1,2), Ryoko Ishikawa (1), Laura Merenda (2), Thomas Wiegelmann (2), Saku Tsuneta (1), Sami K. Solanki (2)
(1) National Astronomical Observatory of Japan (2) Max-Planck-Institute for Solar Sytem Research, Katlenburg-Lindau, Germany
Title: Internetwork horizontal magnetic fields in the quiet Sun chromosphere: results from a joint Hinode/VTT study
Abstract: We present results from a joint Hinode/VTT observing campaign performed in May 2008. Spectropolarimetric data of a quiet Sun supergranular network cell at a heliocentric angle of 56 degrees in the He 10830 line were analyzed using an inversion code involving Hanle and Zeeman effects to retrieve magnetic field strength and direction in the upper chromosphere. Simultaneously recorded Hinode SP data reveal the photospheric magnetic field topology and clearly show the presence of magnetic flux concentrations in the internetwork. The photospheric magnetic field maps are used to feed potential field extrapolations similar to the work by Schrijver and Title (2003). The extrapolated magnetic field topology is compared with the magnetic field configuration directly resulting from the He 10830 inversions. The chromospheric measurements show horizontal magnetic structures extending over a length of up to 20 Mm above the internetwork, indicative for the presence of a magnetic canopy. The photospheric magnetic flux concentrations in the internetwork are obviously not sufficiently strong to prevent the formation of a canopy at chromospheric heights.
References:
Schrijver, C. and Title, A., ApJL 597:L165–L168, 2003
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Jin-Yi Lee, Katharine K. Reeves, Korreck, Kelly E., Leon Golub, K.D. Leka and Graham Barnes
Title: Evolution of magnetic properties for two active regions observed by Hinode/XRT and TRACE
Abstract: We investigate two active regions observed by the X-ray Telescope (XRT) on board Hinode and the Transition Region and Coronal Explorer (TRACE). One shows a constant brightness of the coronal loop in both XRT and TRACE observations. The other shows a brightening in the TRACE observation just after a decrease in X-ray brightness indicating the cooling of the coronal loop. The coronal magnetic topology is derived using the magnetic charge topology (MCT) model for these two active regions applied to magnetograms from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). We discuss the results of the MCT analysis in light of the different coronal emission behavior. This work is funded by the Hinode/XRT contract through SAO, and AFOSR contract FA9550-06-C-0019.
Session: Perspectives on the Physics of Coronal Loops
Authors: Jorrit Leenaarts
Title: MULTI3D - a 3D NLTE radiative transfer code
Abstract: I will present preliminary results from the MPI parallelized radiative transfer code MULTI3D.
Session: Bringing Modeling and Obvservations Together
Authors: K.D. Leka, Ashley Crouch, Graham Barnes
Title: Minimum Energy Method for Resolving the Azimuthal Ambiguity in Hinode/SOT Vector Magnetogram Data
Abstract: WIt has been demonstrated through a series of tests using model data that minimum energy methods are the best available automated techniques to resolve the azimuthal ambiguity that is present in solar vector magnetogram data. We have developed a fast implementation of a minimum energy method that minimizes a combination of the divergence and the current density, following Metcalf (1994). The vertical variation of the field in the divergence and current density is approximated by an extrapolation of the observed boundary. We present in this poster details of application of this code to Hinode/SOT data and demonstrate its use for the Hinode community. This work was supported by funding from NASA/LWS under contract NNH05CC75C and the NWRA subcontract from SAO under NASA NNM07AB07C.
Session: Sunspot Structure and Dynamics
Authors: M. G. Linton
Title: Flare Loop Formation via Magnetic Reconnection
Abstract: Magnetic reconnection is believed to be the key driver of solar flares, and the source of post-flare loops that form below flares. I will present simulations of patchy coronal reconnection in a flare current sheet, focusing on how localized, three dimensional reconnection creates evacuated downflowing loops which form into post-flare arcades in the low corona. I will compare the results with Hinode observations of post flare arcade loops and photospheric flare ribbons.
Session: Flare Physics
Author: :Bruce Lites
Title: Is Flux Submergence and Essential Aspect of Flux Emergence?
Abstract: High resolution Hinode observations of an emerging flux region permit one to examine the detailed structure of the magnetic field vector in emerging flux regions. We find the field to have a concave-upward geometry on the smallest scales observable (0.3"), indicating the presence of U-loops at the sites of approaching and canceling opposite polarities. This structure suggests that reconnection at or below the surface is taking place, allowing the emerging flux to rid itself of the mass that drains into the local dips in the magnetic field. Supersonic down flows are often observed adjacent to, but not coincident with, the sites of canceling flux. We suggest that these are sites that drain the mass contained in the buoyantly-rising flux elements. The observations then suggest that the sub-surface reconnected O-loops descend with convective down flows, thus making flux submergence important to the larger scale flux emergence process.
Session: Solar Magnetic Activity
Authors: Yang Liu
Title: Solar Polar Field Observed by SOHO/MDI and Hinode
Abstract: Using 1-minute cadence, time-series full disk magnetograms taken by SOHO/MDI in a campaign run in 2007 March, and the vector magnetograms taken by Hinode/SOT, we have studied evolutionary characteristics of magnetic elements in solar southern pole. We present here our exploration on relationship between lifetime and flux of magnetic elements, and distribution of element lifetime at high latitude. An attempt to measure differential rotation at high latitude is also made here.
Session: Solar Magnetic Activity
Authors: D.W. Longcope, C.E. Parnell, and A.L. Haynes
Title: The number of magnetic null points in the quiet Sun corona
Abstract: The coronal magnetic field above a particular photospheric region will vanish at a certain number of points, called null points. These points can be found directly in a potential field extrapolation or their density can be estimated from Fourier spectrum of the magnetogram. The spectral estimate, which assumes that the extrapolated field is random, homogeneous and has Gaussian statistics, is found to be relatively accurate for quiet Sun magnetograms from SOHO's MDI. The majority of null points occur at low altitudes, and their distribution is dictated by high wavenumbers in the Fourier spectrum. This portion of the spectrum is significantly affected by Poisson noise, and as many as two-thirds of null points identified from a direct extrapolation can be attributed to noise. The null distribution above 1500 km is found to depend on wavelengths that are reliably measured by MDI in either its low resolution or high resolution mode. After correcting the spectrum to remove white noise and compensate for the modulation transfer function we find that a potential field extrapolated contains, on average, one magnetic null point above 1.5 Mm over every 322 square mm patch of quiet Sun. Analysis of 562 quiet Sun magnetograms spanning the two latest solar minimum shows that the null point density is relatively constant with roughly 10% day-to-day variation. At heights above 1.5 Mm, the null point density decreases approximately as the inverse cube of height. The photospheric field in the quiet Sun is well approximated as that from discrete elements with mean flux 1.0e19 Mx distributed randomly with density 0.007 per Mm. This work supported by NASA LWS
Session: Solar Magnetic Activity
Author: : Tetsuya Magara
Title: Hinode's Observational Result on the Saturation of Magnetic Helicity Injected into the Solar Atmosphere and Its Relation to the Occurrence of a Solar Flare
Abstract: We present a result on the evolution toward the onset of a solar flare, using Hinodefs observations of photospheric magnetic field. Hinode can provide the temporal development of the photospheric field as a vector quantity, which shows that magnetic shear initially developed in a flare-productive active region (AR10930), then it decreased toward the onset of an X-class flare. The magnetic helicity in this active region first increased rapidly, while it became saturated in the late phase. We explain the physical origin of these features in terms of the emergence of a magnetic flux tube into the solar atmosphere, and investigate how it relates to the occurrence of a flare. We also discuss how the magnetic helicity evolves in different types of flares.
Session: Flare Physics
Authors: Sara Martin, Olga Panasenco, and Yashar Agah (Helio Research La Crescenta, CA, USA) Oddbjorn Engvold and Yong Lin, (Institute for Theoretical Astronphysics, Univeristy of Oslo,Norway)
Title: Relating Prominences Observed from Hinode to Known 3-D Structures of Filaments
Abstract: The 3-dimensional structure of the vast majority of prominences (filaments) consist of two interrelated magnetic and plasma structures: (1) extremely narrow, ribbon-like spines confined to curved planes parallel to polarity reversal boundaries in the photosphere and (2) barbs that have one end merged and parallel with the spine and the other gradually deviating sideways from the spine and curving downward to their roots in the chromosphere/photosphere. Both spines and barbs consist of similar fine, parallel or nearly parallel, field-aligned threads of continuously flowing plasma. To relate these structures of filaments seen against the disk to prominence observations above the limb from Hinode, as well as to prominence observations from the ground, is not always a simple task; one must take into consideration the relative visibility of the threads due principally to: (1) their number, plasma density and geometry in the spines and barbs in the various categories of prominences and (2) the column density as seen from various viewing angles, (3) spectral line observed and (4) relative instrument exposure times. Additionally, there are prominences and parts of prominences observed H alpha that have no counterpart in filaments observed in H alpha against the disk. However, a first step in relating limb and disk observations is to map well-observed prominences in three dimensions from observing and tracking the mass motions of their field-aligned threads and groups of unresolved threads from different perspectives afforded as prominences (filaments) transit the solar disk due to solar rotation. A prime example of the disk transit of a large filament is one with visible threads in its spine and very tall barbs as it was observed at Helio Research over an 18-day interval from the first appearance of its top at the east limb until it reached the west limb. This example, along with observations from the Swedish Solar Telescope and other ground and space-based observatories, are used to illustrate how various prominence structures observed from Hinode can be related to the substructures of prominences, i.e., spines and barbs, observed and not observed, in different categories prominences and seen from different viewing angles.
Session: Solar Magnetic Activity
Authors: John T. Mariska
Title: Doppler Shift Oscillations Observed with the EUV Imaging Spectrometer on Hinode
Abstract: Damped Doppler shift oscillations have been observed in emission lines from ions formed at flare temperatures with the Solar Ultraviolet Measurements of Emitted Radiation spectrometer on SOHO and the Bragg Crystal Spectrometer on Yohkoh. Recently, they have also been detected in lines formed at coronal temperatures observed with the EUV Imaging Spectrometer (EIS) on Hinode. I report on additional observations of Doppler shift oscillations in an active region observed in 2007 August. These observations include density-sensitive emission lines from Fe XII and Fe XIII. The oscillations observed with EIS generally have a much lower amplitude than those observed with earlier instruments. This is probably the result of the perturbation that initiates the oscillations being less energetic than the events that produce oscillations in much hotter emission lines. EIS is capable of detecting coronal velocity fluctuations with amplitudes of less than 0.5 km/s with short integration times in strong coronal lines, potentially allowing access to a much richer range of coronal oscillatory phenomena than has been available with earlier instruments.
Session: Perspectives on the Physics of Coronal Loops
Authors: : Cristina Chifor, Alphonse C. Sterling, Helen E. Mason, Ronald L. Moore, Peter R. Young
Title: Evidence for Tether-cutting Leading to a Filament-associated Eruption Observed by Hinode
Abstract: We present Hinode observations of the onset of a solar eruption involving a filament ejection on 2007 May 20. Results from Hinode/SOT, Hinode/XRT and Hinode/EIS have been analysed together with supporting observations from Stereo/SECCHI/EUVI and SoHO/MDI. We observed a converging motion between two opposite polarity sunspots which form the primary magnetic polarity inversion line, along which sits the filament material before eruption. The eruption onset is associated with positive emerging flux canceling repeatedly in a negative polarity region north of the sunspots. We discuss the filament eruption and small scale transient brightenings observed in the onset region prior to eruption. We derive plasma properties from the Hinode/EIS observations. We conclude that the array of observations is consistent with the pre-eruption sheared-core magnetic arcade being gradually destabilised by evolutionary tether-cutting flux cancelation that was driven by converging photospheric flows.
Session: Solar Magnetic Activity
Authors: Satoshi Masuda (STEL, Nagoya University)
Title: Construction of Hinode/XRT flare catalogue
Abstract: In the Yohkoh era, 'The Yohkoh HXT/SXT Flare Catalogue' was created (Sato et al. 2006). It was published as a printed book and is also open at the homepage of Yohkoh/HXT (http://gedas.stelab.nagoya-u.acjp/HXT/). It includes a lot of information, i.e., time, location, GOES time profile, SXT image, HXT 4-bands images, and so on. It was very useful to analyze solar flares statistically and to search events which have some characteristics.
For Hinode, we have just started creating such a catalogue. Since the sun has been quiet for these two years, Hinode have not detected a large number of events. The solar activity will increase in the near future. So it is a good time to start maintaining a flare catalogue. The pointing of Hinode changes more often than that of Yohkoh and the field of view is generally smaller than Yohkoh (HXT always covered the whole sun). The catalogue will be very helpful for researchers to know if some particular event was observed with Hinode or not. Based on the GOES flare list, at first we are checking if XRT observed the flare-occurring region during the flare period. We report the current situation.
Session: Flare Physics
Authors: James McCaughey, Iain Hannah, Kathy Reeves, Paolo Grigis, and Edward DeLuca
Title: The Neupert effect in microflares with Hinode/XRT and RHESSI
Abstract: The Neupert effect, in which the integrated hard X-ray light curve resembles the soft X-ray light curve, is often attributed to flare-accelerated particles heating and evaporating material into hot coronal loops. The Neupert effect has been observed more commonly in larger flares, although it remains unclear whether it is actually less common in microflares or rather is more difficult to detect due to the shorter duration and less intense emissions of microflares. RHESSI provides good temporal resolution of nonthermal hard X-ray emissions and some thermal soft X-ray emissions, while Hinode/XRT provides sensitive, high-resolution imagery of soft X-ray thermal emissions. We use this complementary approach to examine 74 microflares in November and December 2006 with light curves from both XRT and RHESSI. We are investigating the correlation between the presence of an observed Neupert effect and other spectral and morphological characteristics of the microflares. Further research will also aim to better constrain instrumental effects in order to clarify the degree to which the presence or absence of the Neupert effect in microflares can be reliably determined using XRT and RHESSI.
Session: Flare Physics
Authors: David E. McKenzie
Title: Solar Flare Physics in the Hinode Era (Keynote Talk)
Abstract: Hinode's manifest of instrumentation was conceived to investigate the magnetic connections through the photosphere, lower atmosphere, and corona. The complementarity of the instruments is indeed useful, as demonstrated in numerous flares and eruptions in just the first two years of operation. I will review some of the findings from Hinode's observations of flares to date.
It is true, of course, that Hinode's capabilities have evolved since launch. These changes cause the planning of observations to be more complex, and the analysis to be less straightforward; but they do not diminish Hinode's ability to produce important observations of solar flares. On the contrary, Hinode is poised to make truly surprising discoveries. I will explain why this is so, and why we should look forward to the challenge of the coming activity cycle.
Session: Flare Physics
Authors: Scott W. McIntosh
Title: The Inconvenient Truth About Coronal Dimmings
Abstract: We investigate Hinode multi-wavelength high resolution spectro-polarimetric, spectral and broadband images that span the deep photosphere into the corona over the course of a coronal dimming that took place in December 2006. These observations reinforce the belief that coronal dimmings, or transient coronal holes as they are also known, as they are indeed the locations of open magnetic flux in the corona resulting from the launch of a CME. We will see that, as open magnetic regions, they must act just as coronal holes do, only for a considerably shorter span of time - as temporary sources of the fast solar wind. An inescapable question therefore arises - what impact does this source of plasma momentum have on the propagation and in-flight characteristics of the CME that initiates to coronal dimming in the first place?
Session: Source of the Solar Wind/CME
Authors: Scott W. McIntosh, Bart De Pontieu
Title: Connecting Dynamic Phenomena with SOHO/SUMER and Hinode/SOT
Abstract: We will explore the connection of dynamic structure in the chromosphere and transition region using observations from the WHI: Quiet Sun Characterization program of April 2008. In particular, we will study the multi-thermal spectral appearance of spicules in these regions and establish their common magnetic roots.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Author: : Ryan Milligan
Title: Velocity Characteristics of Evaporating Plasma Using Hinode/EIS.
Abstract: Chromospheric evaporation due to nonthermal electrons is commonly believed to be responsible for much of the EUV and X-ray emission observed during solar flares. Observationally this process has been investigated by detecting blueshifts of a single, high-temperature emission line such as the Ca XIX line from Yohkoh/BCS or Fe XIX from SOHO/CDS. With the launch of Hinode, the EUV Imaging Spectrometer (EIS) now offers the opportunity to diagnose this fundamental process over a multitude of high-temperature emission lines, at high spatial, spectral and temporal resolution. The work presented here focuses on how plasma velocities at loop footpoints vary as a function of temperature during the impulsive phase of a C-class flare and possible implications for the standard chromospheric evaporation model.
Session: Flare Physics
Author: : Ryan Milligan
Title: A High-Temperature Microflare Observed With RHESSI and Hinode
Abstract: In this study, data from RHESSI and Hinode are combined to investigate the origin of an unusually high-temperature of 15 MK observed during a B-class event. The absence of any detectable hard X-ray emission coupled with weak blueshifted emission lines suggests that this was a result of direct heating in the corona, as opposed to chromospheric evaporation due to nonthermal electrons. These findings are in agreement with a recent 0D hydrodynamical simulation of microflare plasmas (Klimchuk et al. 2008) which found that a higher continuum temperature can be attained whenever less energy is used to accelerate electrons out of the thermal distribution. In addition, unusual redshifts in the 2 MK Fe XV line were observed cospatial with one of the flare ribbons during the rise phase of the event. As downward flows of such high temperature plasma are not predicted by any known flare model, some possible explanations will be suggested.
Session: Flare Physics
Authors: Urmila Mitra-Kraev, Michael J. Thompson, Alexander G. Kosovichev
Title: Observations of the Sun's Meridional Flow (Invited Talk)
Abstract: The meridional flow is a key ingredient of some solar dynamo models, and may play a crucial role in the 11-year activity cycle of the Sun. The flow is poleward close to the solar surface and must, by mass conservation, turn equatorward deeper down in the convection zone. Helioseismic observations can be used to reveal the flow pattern and its variations. I will give an overview over past observations, and present recent new results on solar cycle-dependent variations of the meridional flow.
Session: Local Helioseismology with Hinode
Authors: Ron Moore
Title: Jet-Front Speed and the Origin of Jets in Polar Coronal Holes
Abstract: The area-average strength of the open magnetic field in the polar coronal holes can be estimated from the radial component of the magnetic field measured by Ulysses in the solar wind, the fraction of the solar sphere covered by the polar coronal holes, and the fraction of the heliosphere filled by the fast solar wind from the polar coronal holes. For the present minimum phase of the solar cycle, the estimated strength is ~ 10 G. Using this strength for the ambient open field in the standard reconnection model for jets in coronal holes, we obtain for any given jet-front speed a lower bound on the initial temperature of the expanding jet-front plasma, and an upper bound on the ambient plasma density at the reconnection site. These two bounds indicate the following. For jet-front speeds ~ 1000 km/s, (1) the reconnection site has to be in the low corona or upper transition region (ne < 10^9 cm^-3), not in the lower transition region or chromosphere, (2) the jet-front plasma is initially heated to T >~ 10^7 K, and (3) hence a compact X-ray flare is produced at the base of the jet. For jet-front speeds <~ 100 km/s, (1) the jet can be produced by reconnection in the lower transition region (~10^9 < ne <~ 10^10 cm^-3) or upper chromosphere (~10^10 < ne <~ 10^12 cm^-3), (2) the initial temperature of the jet-front plasma can be less than 10^6 K, and (3) hence some EUV and H-alpha jet-type macrospicules may be produced with no detectable X-ray emission.
This work is funded by NASA’s Science Mission Directorate through the Heliophysics Guess Investigators Program and the Hinode Mission Operations and Data Analysis Program.
Session: Solar Magnetic Activity
Authors: F. Moreno-Insertis
Title: X-Ray jets in coronal holes: numerical simulation and Hinode observations.
Abstract: Observations with the XRT and EIS instruments onboard Hinode show the appearance of a large number of X-Ray jets in coronal holes, in some cases simultaneously with the emergence of magnetic flux from below the photosphere. We have carried out three-dimensional numerical experiments of the reconnection and jet-launching processes that result from the emergence of magnetic flux from the solar interior into an atmosphere with open field lines, mimicking the situation in a coronal hole. In the experiment, the values of density and magnetic field in the corona are close to those expected in a coronal hole. We combine the results of the 3D numerical simulations with data from the Hinode detectors and show the results of theory and observation to be in excellent agreement.
Session: Bringing Modeling and Observations Together
Authors: Kaori Nagashima, Takashi Sekii, Alexander G. Kosovichev, Junwei Zhao, Theodore D. Tarbell, Saku Tsuneta
Title: Travel-time analyses of an emerging-flux region
Abstract: We report on travel-time analyses of a newly-formed plage region, exploiting high-resolution data provided by Hinode/SOT.
Hinode observed an emerging-flux region (to be NOAA AR 10975) close to the disc centre for 12 hours on 23 November 2007. The SOT observation was in Ca II H line and in Fe I 557.6nm line (Lande g=0); we can use both chromospheric intensity oscillation data and 'non-magnetic' photospheric Dopplergrams for our analyses. The Dopplergrams are not affected by magnetic field and, therefore, are useful in exploring magnetic structure. By cross-correlating oscillation signals, we have detected travel-time anomaly in the plage region. We are currently scrutinising the travel-time measurement method and trying to interpret the anomaly in terms of subsurface structure of this growing active region.
Session: Local Helioseismology with Hinode
Authors: Shin'ichi Nagata
Title: Convective Instability and formation of solar magnetic flux tubes
Abstract: We show the observational evidence for the formation of solar magnetic flux tubes induced by convective instability. Convective instability has been a mechanism used to explain the formation of solar photospheric flux tubes with kG field strength. However, the theory has lacked the observational support for long time. Based on the seeing free observation with Hinode Solar Optical Telescope, we found the cooling of an equipartition field strength flux tube precedes a transient downflow reaching 6 km s-1 and the intensification of the field strength to 2 kG. These observations agree very well with the theoretical predictions.
Session: Solar Magnetic Activity
Authors: Noriyuki Narukage, Ryouhei Kano, Taro Sakao and XRT team
Title: The Thermal Structures of Solar Corona Revealed with Hinode/XRT (Invited Talk)
Abstract: The solar corona has a wide temperature range from less than 1MK (1,000,000K) to more than 10MK. The X-ray telescope (XRT) on board the Hinode satellite has 9 X-ray analysis filters with different temperature responses making it possible to detect both cool and hot coronal plasmas. Using the data observed with this telescope, we can derive coronal temperatures for not only active regions but also quiet regions and coronal holes. Further advantage of XRT is that we can make temperature movies and can investigate time evolution of coronal temperatures. In this talk, we will show some results of our latest studies about the coronal thermal structures. And we will also report the filter calibration results. In this calibration, we also consider the effect of contamination.
Session: Perspectives on the Physics of Coronal Loops
Author: : Zongjun Ning
Title: Evidences of the propagating waves in a prominence Observed by HINODE/SOT
Abstract: We present a quiescent prominence observed by HINODE/SOT on 15 Jan. 2008. It's spines were almost parallel the solar equator. Firstly, consistent with previous observations, numerous thin, thread-like structures are found. Secondly, the prominence exhibits both horizontal and vertical oscillations, which have a typical period of 5 minutes. Such behaviours could be the evidences of propagating wave in prominence. Thirdly, we also find the upflows in the spicule layer from the photosphere to prominence. This indicates one way that the promience materials come from.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: N. Nishizuka, M. Shimizu, T. Nakamura, K. Otsuji, T. J. Okamoto, Y. Katsukawa and K. Shibata
Title: Giant chromospheric anemone jet observed with Hinode and Magnetic reconnection model
Abstract: Hinode discovered a beautiful giant jet with both cool and hot components at the solar limb on 2007 February 9. Simultaneous observations by Hinode/SOT, XRT and TRACE/195A satellites revealed that hot (~5x106 K) and cool (~104 K) jets were located side by side and the hot jet preceded the associated cool jet (~1-2 min.). A current sheet-like structure was seen in optical (Ca IIH), EUV (195A) and soft X-ray emissions, suggesting that magnetic reconnection is occurring in the transition region or upper chromosphere. Alfven waves were also observed with Hinode/SOT. These propagated along the jet at velocities of ~200 km s-1 with amplitudes (transverse velocity) of ~5-15 km s-1, and a period of ~200 s. We performed two-dimensional MHD simulation of the jets on the basis of the emerging flux - reconnection model, by extending Yokoyama and Shibata's model (1995). We extended the model with a more realistic initial condition (~106 K corona) and compared our model with multi-wavelength observations. The improvement of the coronal temperature and density in the simulation model allowed for the first time to reproduce the structure and evolution of both cool and hot jets quantitatively, supporting the magnetic reconnection model. The generation and the propagation of Alfven waves are also reproduced self-consistently in the simulation model.
Session: Solar Magnetic Activity
Authors: : A. Lagerfjärd, Å. Nordlund and R.F Stein
Title: Multi-scale Emerging Flux Simulations
Abstract: We present results of emerging flux simulations on scales of 24x24x20 Mm, carried out with the Copenhagen Stagger Code using a realistic equation of state and radiative transfer with opacity binning. Using two complementary types of experiments we study the spontaneous creation of (loop-) structures on scales ranging from granular to near-supergranular. One type of experiment starts out from a dynamically and thermally relaxed convection simulation with no magnetic fields, with an open lower boundary condition where up-flows carry an approximately uniform horizontal field. Over time (many solar hours) a characteristic power law distribution of magnetic field strength with depth develops, with amplitudes scaling approximately as the square root of density. Another type of experiment starts out from an approximation to the final distribution and converges faster towards that distribution. The final distribution contains a hierarchy of loop structures, with the strongest and largest scale ones reminiscent of small active regions.
Session: Solar Magnetic Activity
Authors: : Joten Okamoto and SOT core team
Title: Emergence of a Helical Flux Rope and Prominence Formation
Abstract: Previous statistical studies indicate that numerous prominences have the so-called inverse-polarity magnetic configuration suggesting the helical magnetic configurations. However, the formation process of helical magnetic configuration in prominences remains unclear. In order to study the formation process of prominences, we obtained continuous observations of a prominence in NOAA AR 10953 with the Solar Optical Telescope. We found evidence that a helical flux rope emerged from below the photosphere under a pre-existing prominence. After this helical flux rope emerged, the pre-existing prominence became stable. We suggest that this supply of a helical magnetic flux into the corona is associated with formation and maintenance of active-region prominences.
Session: Solar Magnetic Activity
Author: :Ramon Oliver
Title: Transverse oscillations of flowing prominence threads observed with Hinode: fast of Alfven?
Abstract: Recent observations with the Hinode Solar Optical Telescope display an active region prominence whose fine threads oscillate in the vertical direction as they move along a path parallel to the photosphere. A seismological analysis of this event is carried out by taking advantage of the small radius of these structures compared to the total length of magnetic field lines, i.e. by using the thin tube approximation. This analysis reveals that the oscillations are caused by kink (i.e. fast) waves, that their period is only slightly modified by the existence of the flow, and that the difference between the period of a flowing thread and a static one is below the error bars of these observations. Moreover, although it is not possible to obtain values of the physical parameters, a lower bound for the Alfv\'en speed (ranging between 120 km s$^{-1}$ and 350 km s$^{-1}$) is obtained for each of the threads. Such Alfv\'en speeds agree with the intense magnetic fields and large densities usually found in active region prominences.
Session: Bringing Modeling and Obvservations Together
Authors: David Orozco Suárez (Invited Talk)
Title: Simulation and analysis of Hinode spectropolarimetric observations
Abstract: The diffraction-limited observations of the Hinode spectropolarimeter have open exciting possibilities for the analysis of the weak magnetic signals of the solar internetwork (IN). Hinode/SP has demonstrated that the IN is permeated by highly inclined fields with weak flux densities. It has allowed us to analyze the emergence, evolution and disappearance of small-scale flux concentrations that occur in form of loops in the photosphere. These observations of the IN are important to solve the discrepancy between the field strength distributions obtained using visible and infrared ground-based measurements. Recently, it has been argued that the information contained in the Fe I 630 nm spectral region is not sufficient to provide reliable field strength values. In this contribution, radiative magnetoconvection simulations are used to generate Hinode/SP observations, in an attempt to examine the reliability of Milne-Eddington (ME) inversions applied to very high spatial resolution data. The results show that ME inversions deliver reasonably good magnetic field strengths and inclinations from Hinode/SP measurements, provided the effects caused by telescope diffraction are corrected. These effects can be well modeled using a local stray-light contamination. If one does not account for the reduction in polarization signals caused by diffraction, the inversion leads to field strengths that are too weak.
Session: Bringing Modeling and Obvservations Together
Authors: Ada Ortiz Carbonell
Title: Polarimetry at the SST: CRISP
Abstract: CRISP, the new spectropolarimeter installed at the Swedish Solar Telescope, opens a new perspective for solar polarimetry studies. With better spatial resolution than Hinode in the Fe I 6302 line and similar polarimetric sensitivity, complements (after postprocessing of the data) the SP spectropolarimeter onboard Hinode.
Session: Bringing Modeling and Obvservations Together
Author: : Spiros Patsourakos
Title: Hot Spectral Emissions in Quiescent Active Regions and Nanoflare Heating
Abstract: A leading candidate for the heating of active region (AR) coronal loops is the nanoflare model. This model treats coronal loops as collections of impulsively heated sub-resolution strands and explains several key observational aspects of warm (1-2 MK) coronal loops. However, the basic requirement of this model is that the strands initially reach very high temperatures of several MK before they cool down to canonical coronal temperatures. Therefore, the detection of hot plasmas in AR loops represents a stringest test of the nanoflare model. Previous work has shown that the best way to observe the postulated hot plasmas is by the means of spectroscopic observations in hot lines (T > 3 MK). The emission is predicted to be quite faint, but the EIS spectrometer onboard Hinode has sufficient sensitivity to allow us to perform such a test for the first time. We will present an analysis of the emission characteristics of quiescent coronal loops in a number of hot lines spanning approximately 3-12 MK (Ni XVII, Ca XV, Fe XVII, Ca XVII, Fe XXIII). We will show that hot plasmas are ubiquitous over entire active regions, and we will compare the measured intensities of both hot and warm lines with predictions of nanoflare models.
Session: Perspectives on the Physics of Coronal Loops
Authors: Olga Panasenco (Helio Research), Marco Velli (JPL CalTech), Thomas Berger (LMSAL)
Title: PLASMA MOTIONS IN PROMINENCES OBSERVED BY HINODE/SOT
Abstract: We analyze the plasma motions inside prominences observed by Hinode/SOT during 2006-2007 with focus on two spectacular examples from 25 April 2007 in H-alpha line and 30 November 2006 in CaH line. It is now well-known that most filaments (prominences on the limb) are composed of fine threads of similar dimensions rooted in the chromosphere/photosphere. Recent observations of counter-streaming motions together with oscillations along the threads provide strong evidence that the threads are field aligned. To more correctly interpret the nature of observed downward flows of dense and cool plasma as well as the upward dark flows of less dense plasma, we take into account the geometry of the prominence structures and the viewing angle. The dark upflows exhibit turbulent patterns such as vortex formation and shedding that are consistent with the motions predicted by instabilities of the interchange type. Sometimes an appearance of dark motions is generated by dark voids opened in the prominence sheet after initiation of nearby downflow streams, implying mass drainage in the downflows. Based on 304Å observations, there is more filament mass in prominences than is visible in either the H-alpha or CaH lines. The source of the downward moving plasma may be located either higher above the visible upper edge of the prominence or on the far end of the prominence spine. The bright downward motions of the more cool and dense plasma may be partly due to the counter-streaming motion along the magnetic fields lines, and partly to the presence of Rayleigh-Taylor type or ballooning/interchange instabilities in the upper regions of the prominence. We suggest that combination of flows along field lines, shear, and unstable stratification may provide the answers to the intriguingly elegant motions seen in prominences.
Session: Solar Magnetic Activity
Authors: S. Patsourakos, J. A. Klimchuk
Title: EIS Observations of Hot Emissions in Quiescent Active Regions and Nanoflare Heating
Abstract: A leading candidate for the heating of active region (AR) coronal loops is the nanoflare model. This model treats coronal loops as collections of impulsively heated sub-resolution strands and explains several key observational aspects of warm (1-2 MK) coronal loops. However, the basic requirement of this model is that the strands initially reach very high temperatures of several MK before they cool down to canonical coronal temperatures. Therefore, the detection of hot plasmas in AR loops represents a stringest test of the nanoflare model. Previous work has shown that the best way to observe the postulated hot plasmas is by the means of spectroscopic observations in hot lines (T > 3 MK). The emission is predicted to be quite faint, but the EIS spectrometer onboard Hinode has sufficient sensitivity to allow us to perform such a test for the first time. We will present an analysis of the emission characteristics of quiescent coronal loops in a number of hot lines spanning approximately 3-12 MK (Ni XVII, Ca XV, Fe XVII, Ca XVII, Fe XXIII). We will show that hot plasmas are ubiquitous over entire active regions, and we will compare the measured intensities of both hot and warm lines with predictions of nanoflare models.
Session: Perspectives on the Physics of Coronal Loops
Authors: :D. Pérez-Suárez, R.C. Maclean, J.G. Doyle, M.S. Madjarska
Title: The Structure and Dynamics of a Bright Point as seen with Hinode, SoHO and TRACE
Abstract: We present a study of two Coronal Bright Points where data from Hinode, SoHO and TRACE are analysed. Covering a large temperature range, we study the variation of the BP from the surface to the corona investigating both the morphology and variation in physical parameters, such as electron density, Doppler-shift and magnetic field variability. We obtain excellent correlation between the X-ray light curve with the positive magnetic flux; also a good agreement is found between a potential extrapolated magnetic field and the loops seen in the X-ray images.
Session: Solar Magnetic Activity
Authors: A. Pietarila, R. Cameron, S.Solanki
Title: Expansion of magnetic flux concentrations with height: a comparison of Hinode NaD SOT data and MHD simulations
Abstract: Contribution functions of the Hinode SOT NaD BFI filter show that most of the signal originates from the photosphere. The formation height of the filter signal increases somewhat as one approaches the solar limb. We utilize this feature of the SOT NaD data to study the expansion of magnetic flux concentrations with height. We study how the appearance (such as size and whether the feature is unipolar or bipolar) of flux concentrations seen in NaD Stokes V filtergrams changes from disk center to limb. The Hinode data are compared to synthetic data from 2D (24 Mm horizontal, 1.7 Mm vertical) radiative MHD simulations to see how well the expansion of magnetic flux with height is captured by the simulations. We do this study using two different top boundary conditions for the magnetic field: vertical and potential. Preliminary results from a comparison to a 3D simulation are also given.
Session: Bringing Modeling and Obvservations Together
Authors: : Jonathan Pietarila Graham, Sanja Danilovic, Robert Cameron, Manfred Schuessler, Alexander Voegler
Title: The Solar Surface Dynamo (Keynote Talk)
Abstract: Small-scale photospheric fields are even less well understood than the large-scale, global solar magnetic field. These small-scale fields are likely generated by a dynamo process variously called the turbulent, small-scale, local or "fast" dynamo. This dynamo is well-studied in idealized simulations but not so in solar-like conditions where the low magnetic Prandtl number and the complexities of solar convection could alter, or stop, this process. In this talk we present results from the radiative magnetoconvection MURaM code which demonstrate that stratified, compressible, non-helical surface convection without enforced recirculation is capable of turbulent local dynamo action near the solar surface. This dynamo action is contrasted with idealized simulations through a spectral transfer analysis. We compare MURaM simulation results and Hinode observations. We find the ratio between the averaged horizontal and vertical field components to be consistent with the values derived from Hinode. We demonstrate the fractal (self-similar) nature of the cancellation of Stokes V signals produced by opposite polarity magnetic fields on scales smaller than observational resolutions. Utilizing both simulations and Hinode observations, we provide estimates of the mean unsigned magnetic flux of the photosphere.
Session: Bringing Modeling and Obvservations Together
Authors: : N.-E. Raouafi
Title: On the relationship between coronal jets and plumes
Abstract: We report on x-ray and extreme ultraviolet (EUV) observations to study the relationship between coronal jets and plumes. Hinode/XRT and STEREO/SECCHI/EUVI data is utilized. We find that $>90\%$ of the identified jets are directly related to plumes. EUV data shows that plume haze rise from the same spatial location of more than $70\%$ with a time delay ranging from minutes to hours. The remaining jets occurred in areas where plume material exists already. The latter is enhanced of after the jet eruption. Short-lived jet-like events and small transient bright points are seen at different locations within the base of pre-existing long-lived plumes. X-ray images also show instances of rapid evolution of collimated-thin jets to much wider plume-like structures associated with the delayed appearance of plume haze in the EUV. These observations suggest evidence for x-ray jets being precursors of polar plumes or of brightness changes in plumes.
Session: Solar Magnetic Activity
Authors: : N.-E. Raouafi
Title: EVOLUTION OF A CORONAL TWISTED FLUX ROPE: FILAMENT FINE STRUCTURE
Abstract: Multi-instrument data sets of NOAA AR10938 on 2007 Jan. 16 (Hinode, STEREO, GOES, ISOON H$\alpha$, ..) are utilized to study the fine structure and evolution of a highly twisted coronal flux rope. The footpoints of the magnetic threads are closely rooted into pores and plage areas. A C-class flare recorded by GOES at approximately 2:35 UT near one of the rope footpoints (along with a wisp of loop material shown by EUV data) led to the brightening of the flux rope revealing its fine structure with several threads showing high degree of linking ($\sim180\degr$-left-handed helical). EUV observations by Hinode/EIS of hot lines show a complex structure of coronal loops. The same features were observed about 30 minutes later in X-ray images and about 30 minutes further in EUV images of STEREO/SECCHI/EUVI with much better resolution. H$\alpha$ and STEREO/SECCHI/EUVI 304~{\AA} images revealed the presence of several filament fibrils in the same area. They evolved a few hours later into a denser structure seemingly showing helical structure, which persistently lasted for several days forming a segment of a larger scale filament. This is a direct observational evidence for resolved fine structure of a highly twisted flux tubes leading to the formation of a solar filament.
Session: Perspectives on the Physics of Coronal Loops
Authors: : Fabio Reale, Jim Klimchuk, Susanna Parenti, Paola Testa
Title: XRT Detection of Hot Plasma in Active Regions and Nanoflare Heating
Abstract: Nanoflares occurring in sub-resolution strands have been long invoked as strong candidates for the heating of active region (AR) coronal loops. However, the frequent occurrence of nanoflares requires the steady presence of flare-hot plasma in the active region, which has been difficult to detect so far. We report on the analysis of multi-filter Hinode/XRT observations of an active region, which shows the widespread presence of ~10 MK plasma. XRT diagnostics allow us to estimate that the amount of hot plasma is compatible with models of AR coronal loops as bundles of nanoflaring strands.
Session: Perspectives on the Physics of Coronal Loops
Authors: Reardon K., Rimmele T., Tritschler A., Cauzzi G., Woeger F., Uitenbroek H., Tsuneta T., Berger T.
Title: Open Access to Targeted Ground-Based Observations for Hinode Collaborations
Abstract: The seeing-free, long-duration, observations available from Hinode have been a boon to solar physics. Ground-based observations still have notable advantages however, including significantly higher data rates, additional spectral diagnostics, and greater flexibility. Significant advances can be made by combining both ground-based and space-based data.
However, ground-based observations, because of their changing instrumental configurations and the random effects of weather and seeing, have traditionally been less efficient than satellite observations in producing useful data. Investigators are typically required to be present at the telescope and learn the intricacies of the instrumentation in order to obtain and analyze the desired data. It is clear, in particular given the experience with Hinode, that this situation will need to change to maximize both scientific output and operational efficiency.
We describe a program recently begun at the National Solar Observatory to provide open access to investigator-driven, ground-based data through the designation of "service-mode" observing periods. During these times, the facility instrumentation of the Dunn Solar Telescope is made available to external requests that are part of joint Hinode observing programs. Multiple programs covering a range of solar targets are proposed, with each principal investigator specifying the type of data they desire. The choice of target each day is based on the solar conditions, allowing a more optimized used of the ground-based solar facility. When a successful data set is obtained, it is reduced by the NSO staff and provided in a processed form to the external investigator.
We have conducted several such service-mode periods at the DST using the IBIS, providing several end users with fully reduced, imaging-spectroscopy data. We will present examples of the joint datasets obtained as part of this program and describe how Hinode users can participate in future service-mode observing periods.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Reardon K., Tritschler A., Katsukawa, Y.
Title: Spectroscopic Properties of Penumbral Transients
Abstract: Observations with Hinode/SOT recently revealed the presence of rapid, small-scale brightenings in sunspot penumbrae identified in running difference images of Ca II H filtergrams. These events have been termed penumbral microjets (PMJ) and are thought to be the result of reconnection in the interleaved magnetic fields of the penumbra.
We investigate the nature of these events by combining SOT/BFI images with simultaneous imaging spectroscopy data in the Ca II 8542 line obtained with IBIS at the Dunn Solar Telescope. We observed AR10905 for 30 minutes on 28 August 2007 and obtained repeated scans of the Ca II spectral profile with a 5.8 second cadence. With the high temporal and spatial resolution of both the Hinode and IBIS data, we are able to identify numerous impulsive brightenings. Studying the spectral signatures of these events allows us to better probe the mechanisms that produce the observed intensity enhancements. We find that transient penumbral brightenings exhibit a variety of signatures indicating that multiple physical processes, both acoustic and magnetic, might be at work to produce different classes of these small scale events.
In some of the more prominent events, we identify a spectral signature similar to Ellerman bomb profiles. These profiles have strong enhancements in the line wings, but little response in the chromospheric core. We examine what processes might produce such a line profile and the role of the complex chromospheric magnetic field in the overall penumbral dynamics.
Session: Sunspot Structure and Dynamics
Authors: : Reeves Kathy
Title: DEM Temperature Analysis of Post-Flare Loops Using Hinode's X-Ray Telescope
Abstract: We investigate the temperature structure of the post-flare loops from several small flares by utilizing a differential emission measure (DEM) method that takes advantage of the many X-ray filters available on the X-Ray Telescope (XRT) on Hinode. This method allows us to observe multi-thermal plasma along the line of sight. Using this method, we see clear evidence of multiple temperatures in the post-flare loops systems, and we compare the observed cooling times to calculated values. Additionally, we find that there are temperature structures derived from the DEM method that are not obvious from the observed intensities alone.
Session: Flare Physics
Authors: M. Rempel, M. Schuessler, M. Knoelker
Title: MHD simulations of sunspot fine structure (Invited Talk)
Abstract: We present results from 3D MHD simulations of sunspots carried out with the MURaM MHD code. The largely relaxed state of the sunspot shows a division in a central dark umbral region with bright dots and a penumbra showing bright filaments of about 3 to 4 Mm length with central dark lanes. By a process similar to the formation of umbral dots, the penumbral filaments result from magneto-convection in the form of upflow plumes, which become elongated by the presence of an inclined magnetic field: the upflow is deflected in the outward direction and bends down the magnetic field to become almost horizontal in the upper part of the plume near the level of optical depth unity. At the same time, roll-type motion leads to a flow perpendicular to the filament axis and to downflow near its edges. Expansion and flux expulsion leads to a strong reduction of the field strength in the upper part of the rising plume, where a dark lane forms owing to the piling up of matter near the cusp-shaped top and the upward bulging of the surfaces of constant optical depth. The simulated penumbral structure corresponds well to the observationally inferred interlocking-comb structure of the magnetic field with Evershed outflows along dark-laned filaments with nearly horizontal magnetic field and roll-type perpendicular motion, which are embedded in a background of stronger and less inclined field. Photospheric spectral lines are formed at the very top and somewhat above the upflow plumes, so that they do not fully sense the strong flow as well as the large field inclination and significant field strength reduction in the upper part of the plume structures.
Session: Sunspot Structure and Dynamics
Authors: Francois Rincon
Title: Supergranulation and TFGs evolution from HINODE observations
Abstract: From HINODE/SOT NFI (NarrowBand Filter Imager) and BFI (Broadband Filter Imager), a long time-sequence has been recorded continuously at the disk center from 29 August (10:17 UT) to 31 August (10:19 UT) 2007. A 3D analysis (x,y,t) of the granular intensity field demonstrates that a significant fraction of granules in the photosphere are organized in Trees of Fragmenting Granules (TFGs). TFGs are families of repeatedly splitting granules, originating from a single granule at their beginning. Using a two-days time series enables us to characterize their evolution on the timescale of supergranulation and to study how they affect the distribution of magnetic elements in the quiet Sun.
We observe that most of the granules visible on the Sun's surface belong to long-lived TFGs, and that these families strongly structure surface flows. Different TFG evolutions observed in our field of view show that two important collective TFGs behaviours contribute to the redistribution of passive corks up to supergranular cell scales. The first one is the combined action of successive TFGs born at a given location, which gives rise to structures at classical mesoscales. The second one is the common action of two or more long lived TFGs born more or less at the same time, that sweeps corks to network scales.
Following the time evolution of passive corks and magnetic elements (see movies at http://www.lesia.obspm.fr/~malherbe/papers/Hinode2008/) reveals that both are advected by long-lived TFGs, and that their distribution coincides with the supergranular network. This observed co-spatiality between magnetic elements and corks in our time sequence analysis therefore demonstrates that the distribution of magnetic fields and the evolution of the magnetic network are strongly influenced by TFGs on the Sun's surface.
Session: Solar Magnetic Activity
Authors: Margarita Ryutova
Title: Response of Chromosphere to Penumbral Dynamics: Bow Shocks
Abstract: We present observations of sunspot penumbrae obtained during the disc passage of AR 10923 (November 10-20, 2006) with the SOT instrument on Hinode in G-band and Ca II H line. Along with recently discovered jetlike features (Katsukawa et al 2007), we find other kinds of bright elongated transients abundantly pervading the entire penumbra and drifting as a whole in a direction almost perpendicular to their long axes. We present quantitative analysis of these features and interpret them relative to our recent penumbral model (Ryutova, Berger and Title 2007) to show that they are produced by shocks resulted from a sling-shot effect associated with the on-going reconnection processes in neighboring penumbral filaments. Due to sharp stratification of the low atmosphere, post-reconnection flux tubes moving upward, quickly accelerate. At transonic velocities a bow shock is formed in front of the flux tube, as usually occurs in cases of blunt bodies moving with supersonic velocities. Observed parameters of transients are in good agreement with calculated parameters of bow shocks. On some, much more rare occasions compared to ``drifting'' - bow shock type transients, there appear compact bright transients moving in radial direction, along their long axis, and having velocities of 20 - 50 km/s. We relate these features to a category of true microjets.
Session: Sunspot Structure and Dynamics
Authors: Margarita Ryutova
Title: Formation and Dynamics of Multi-Thread Arcades of Coronal Loops
Abstract: The post-flare coronal loops having well defined filamentary structure, often appear as an arcades of thin magnetic threads resembling winding in a curved solenoid. Compared to flare timescales, post-flare arcades are long living, well organized structures. Elemental filaments in arcades are, however, in highly dynamic state, harboring frequent microflares, which often appear with strict regularities. And questions are: How the multi-thread arcades are formed? Why they live so long? What determines the spatial and temporal regularities of microflares? What role is played by underlying magnetic activity? We address these questions using observations obtained with the SOT and XRT instruments on Hinode, combined with the TRACE 195 coronal line. The basic object of observations is the December 13, 2006 activity.
Session: Perspectives on the Physics of Coronal Loops
Authors: Margarita Ryutova
Title: Sunspot Penumbrae: Formation, Evolution and Fine Structure
Abstract: We present the observations of sunspot penumbrae, and propose a mechanism that explains the fine structure of penumbral filaments, their observed dynamics, and their formation process associated with the evolution of sunspot. The mechanism assumes that the umbra itself is a dense conglomerate of non-collinear interlaced flux tubes. On-going reconnection processes in such a system lead in the first place, to branching out of the peripheral filaments from the ``trunk'' with different inclinations and at different heights. Most importantly, each elemental act of reconnection facilitates the onset of a screw pinch instability in reconnected flux tubes, which in turn determines the distribution of electric currents, helical magnetic fields, and temperature inside the filaments. Almost all the parameters in theory are directly observable, and are in good agreement with the observation. At the same time, due to special conditions in the photosphere, e.g. finite plasma beta, sharp stratification, etc., reconnection and post-reconnection processes lead to multi-step events that in a proper time scales manifest themselves in the chromospheric microjets and bow shocks, all being in good qualitative and quantitative agreement with the observations.
Session: Sunspot Structure and Dynamics
Authors: : Jun-ichi Sakai and Philip Smith
Title: Two-fluid simulations of coalescing penumbra filaments driven by neutral hydrogen flows
Abstract: We investigate magnetic reconnection rates during the coalescence of two penumbra filaments with axial flows in the solar photosphere, by altering the initial colliding velocity of neutral hydrogen and axial current intensity. We used a newly developed two fluid (ion-neutral) numerical code that is developed from the Artificial Wind scheme. The existence of the axial flow in the penumbra filament does not affect the magnetic reconnection. It was found that the magnetic reconnection rates are strongly affected by the inclusion of the initial neutral colliding flow velocity as well as the axial current intensity. The ions can be heated up to about 40- 100 times of the initial temperature by both collisional and Ohmic heating, while the neutral hydrogen is very weakly heated.
Session: Sunspot Structure and Dynamics
Authors: Taro Sakao, Noriyuki Narukage, and Ryouhei Kano
Title: Evolution of Temperature and Magnetic Structure of the Corona Observed with Hinode XRT
Abstract: We report dynamic evolution of temperature structure of the X-ray corona observed with the X-Ray Telescope (XRT) aboard Hinode. XRT is equipped with a set of thin metal filters (focal-plane analysis filters) that are inserted selectably in the optical path, with which filter-ratio temperature maps can be obtained. This capability, coupled with high-cadence imaging performance of XRT, enables us to investigate dynamic evolution of temperature structure of the corona in a wide fied-of-view, with high time resolution (e.g., obtaining a temperature map in, say, every 1 minute, or even higher).
A wide area on the Sun (742.4 Mm square), centered at a decaying active region (labeled as NOAA AR 10988 in the previous rotation) on 24 April 2008, was subjected to such an investigation for a duration of 3.5 hours. A notable feature observed was that there was a clear signature of monotonically-decreasing temperature, from 2.0 MK to 1.7 MK in about 2 hours, in a region at, or close to, the edge of the decaying active region. A preliminaly analysis indicates that this region corresponds to the footpoint area of cool loops seen in the 171 A band of SOHO/EIT and STEREO/SECCHI that showed evolution in structure in association with the temperature decrease seen with XRT.
XRT observations on such temperature evolution of the corona will be presented and its relationship with the evolution of magnetic field structure in the corona discussed.
Session: Perspectives on the Physics of Coronal Loops
Authors: Aveek Sarkar; Robert W Walsh
Title: Coronal loops as multi-stranded, impulsively-heated magnetic elements: observational signatures and consequences for Hinode, STEREO and SDO
Abstract: There is a growing body of evidence that the loops seen with current instrumentation SOHO, TRACE and Hinode may consist of many sub-resolution elements. Thus, the total emission we observe is the combined radiation of many evolving plasma strands. We present a "global loop" as 125 individual strands, with each modelled independently by a one-dimensional hydrodynamic simulation. The energy across the strands is released in nanoflares - localised, discrete heating events - and the strands are "coupled" through the frequency distribution of this energy input which follows a power law. In particular, we will demonstrate the consequences of employing this modelling approach on the puzzling observations of loop over-densities, persistent red-shift downflows, filter ratio isothermality and observed EM loci distributions. Specifically, we will show that ALL of the above can be explained from a multi-strand perspective and hence from this, make predictions for observations for the up-coming SDO mission.
Session: Perspectives on the Physics of Coronal Loops
Authors: Sabrina Savage and David E. McKenzie
Title: Detecting and Measuring Reconnection Outflows in the Hinode Era
Abstract: Our aim has been to provide direct quantitative measurements of reconnection signatures during solar flaring events in order to constrain the properties of flare energetics. Reconnection outflows are observed as sunward-flowing voids during long-duration flares, consistent with 3D reconnection models. Through the use of our automatic detection software, we have obtained trajectories, velocities, sizes, and magnetic flux information for outflows seen in several flares from various instruments. Several limitations have been encountered with instruments prior to the availability of Hinode, and it is the purpose of this work to show the progress we have made in detecting reconnection signatures in the form of supra-arcade downflows (SADs) and to emphasize the potential of making better detections and measurements with Hinode's X-ray telescope (XRT).
Session: Flare Physics
Authors: G. Scharmer
Title: New Capabilities for High Resolution Collaborative Studies with the Swedish 1-m Solar Telescope
Abstract: The high spatial resolution of Hinode spectropolarimetric data represents a break-through in our ability to observ magnetic fine structures in and outside sunspots. In spite of development of adaptive optics, a similar spatial resolution has so far not been achieved with spectrograph-based spectropolarimeters on any ground-based solar telescope. We have recently installed a filter based spectropolarimeter, CRISP, at the SST. Using short exposures and image reconstruction techniques, this system allows high cadence (30 s) excellent S/N (1000:1) scans at 10-12 wavelengths in the 6302 Fe I lines with a spatial resolution approaching 0.15 arc sec. Whereas time sequencies with such spatial resolution will be rare, the possibility of occasional simultaneous observations with Hinode with allow valuable evaluation of limitations from reduced spectral content on one hand (SST) and lower spatial resolution on the other hand (Hinode). CRISP can be used at virtually any wavelength from 510 nm to 860 nm with adequate pre-filters. We show also examples of observations made at 5381, H-alpha and Ca II 8542 to demonstrate its potential.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Rolf Schlichenmaier
Title: The small-scale net circular polarization in sunspot penumbrae
Abstract: The net circular polarization, NCP, is the integral of the Stokes V profile of a spectral line. It can only be non-zero if velocity gradients exist along the line of sight. At a spatial resolution of some 1 arc sec NCP maps of penumbrae show peculiar symmetry properties. These properties have successfully been reproduced with a penumbra that consists of flow channels that are more inclined than a background magnetic field, supporting the concept of an uncombed penumbra and the moving tube model. For these models it was essential that the inclination of the magnetic field and the velocity changes along the line of sight according to an essentially horizontal flow channel embedded in a less inclined magnetic field of the same magnetic field strength as the flow channel.
With the advent of spectro-polarimetry at a spatial resolution of better than 0.5 arc sec, the small-scale variations of the NCP could be measured. It becomes apparent that for certain heliocentric angles the upper model leads to inconsistencies. In this poster we will elaborate on these inconsistencies and present possible solutions to the dilemma. As one possibility we demonstrate that differences in the magnetic field strength between the flow channel and the background could reconcile the uncombed model with the observations. From these considerations we find that in the outer penumbra, the magnetic field strength of the flow channel is stronger than in the surroundings.
Session: Sunspot Structure and Dynamics
Authors: Donald Schmit, Sarah Gibson, Scott Macintosh, Terry Kucera, David Brooks, Alphonse Sterling, Durgesh Tripathi
Title: Prominence Cavities in EIS
Abstract: Recent observational campaigns have brought together a wealth of data specifically designed to explore the physical properties and dynamics of prominence cavities. In particular, STEREO and Hinode data have provided new perspectives on these structures. Using EIS data, we examine the morphological differences observed in the prominence, cavity core, and rim over a range of lines spanning Fe VIII to Fe XIV. DEM analysis is also performed using CHIANTI with the goal of understanding the temperature gradient between the cavity and the surround quiet sun plasma.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Takashi Sekii
Title: High-resolution Helioseismic Observations (Invited Talk)
Abstract: I am reviewing helioseismic observations made by Hinode Solar Optical Telescope (SOT) as well as discussing how best we can exploit from now on the high-resolution capability of SOT for studying solar sub-surface structure and flow, particularly in the era of SDO/HMI.
Session: Local Helioseismology with Hinode
Authors: Selhorst, Caius L., Silva-Válio, Adriana, Costa, Joaquim E. R.
Title: 17 GHz active region model using magnetogram extrapolation
Abstract: In order to reproduce the radio observations from Nobeyama Radioheliograph (17 and 34 GHz), a 3-D solar atmospheric model was constructed considering the thermal bremsstrahlung and gyro-resonance emission mechanisms. To estimate the magnetic field struture in the solar atmosphere, we extrapolated photospheric magnetograms (MDI mainly) considering potential and force-free magnetic field extrapolations. The changes in the quiet Sun atmosphere (density and temperature distributions) due to the interaction with magnetic field was considered. Our model showed the following results for highly polarized 17 GHz active region: a) the intensity of the MDI magnetograms is able to account for the emission as gyro-resonance, however, the problem with saturation points still persists; b) for a low number of saturation points, a simple linear correction could change the maximum brightness temperature results completely; c) the brightness temperature maxima results have a excellent correspondence with the observed values; and d) the spatial distribution of the gyro-resonance emission was well-reproduced either by a potential or force-free field extrapolation. At 34 GHz, the emission was successfully modeled as completely free-free radiation with a brightness temperature maximum in agreement with the observations.
Session: Solar Magnetic Activity
Authors: : Kiyoto Shibasaki
Title: A Driving Mechanism of Temperature Dependent Plasma Up-Flows in the Solar Corona
Abstract: One of the most important finding by HINODE is plasma up-flows in the solar corona. Sakao et al. (2007) found plasma up-flows in an open magnetic field region by XRT. These flows were confirmed by the EIS Doppler measurement (Harra et al., 2008). Imada et al. (2007) found by EIS, temperature dependent plasma up-flows in the unipolar magnetic field region during the declining phase of the X-class flare on December 13, 2006. Plasmas hotter than 1MK show up-flows while the cooler ones do not. Temperature dependent plasma up- and down- flows are also found by Peter & Judge (1999) in the quiet sun and coronal holes. The critical temperature which divide up- and down- flows is 0.5 MK for both regions. We propose a very simple and robust mechanism to drive temperature dependent plasma flows and explain how the critical temperature is determined.
Charged particles moving in the magnetic filed have magnetic moment caused by gyration motion due to Lorenz force. The magnetic moments are directed anti-parallel to the surrounding magnetic field. Hence, thermal plasma particles in the solar corona should be treated as diamagnetic dipoles rather than charged particles. If thermal equilibrium is established among charged particles, magnetic moment of each particle is proportional to the temperature and is inversely proportional to the magnetic field (\mu=kT/B) and is independent of the charge and the mass. In the magnetic field gradient, diamagnetic dipoles are pushed toward weak field region (f = - \mu dB/dr). As the result, the force is proportional to the temperature and is inversely proportional to the magnetic scale length (L=1/{(1/B)(dB/dr)}). Generally, magnetic field strength decreases upwards, hence this force is directed upwards. If this magnetic force exceeds gravity force, plasma up-flow is expected. The critical temperature is determined by the balance between the gravity force and the magnetic force. In the case of magnetic scale length with active region size, the critical temperature is about a million degree.
Session: Source of the Solar Wind/CME
Authors: : K. Shibata
Title: Ubiquitous magnetic reconnection in the solar atmosphere
Abstract: Recent space observations of the Sun with Yohkoh, SOHO, TRACE, and RHESSI revealed that magnetic reconnection is ubiquitous in the solar corona, ranging from small scale reconnection (nanoflares) to large scale one (CME related flares). These reconnection events are often associated with mass ejections with various sizes, from jets to CMEs. Recent Hinode satellite has revealed also that magnetic reconnection is ubiquitous in the solar chromosphere, and that even smaller reconnection events occur in the solar chromopshere, which are associated with tiny jets called chromospheric anemone jets. These observations imply that the solar atmosphere consists of self-similar dynamical structure, i.e., fractal structure, which is consistent with basic magnetohydrodynamics (MHD) theory, since MHD does not contain any characteristic length and time scale, and it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection, and discuss possible implication to coronal heating, reconnection physics, and particle acceleration.
Session: Bringing Modeling and Observations Together
Authors: T.Shimizu (ISAS/JAXA) and the Hinode SOT core team
Title: Hinode observation of the vector magnetic fields in a sunspot light bridge accompied by chromospheric plasma ejections
Abstract: We present high resolution magnetic field measurements of a sunspot light bridge (LB) in NOAA Active Region 10953 taken with Solar Optical Telescope on 2007 April 29 and 30. Simultaneous imaging observations with chromospheric lines (Ca II H and H alpha) show that upward plasma ejections occurred intermittently and recurrently from the LB on April 30, whereas plasma ejections were less observed on April 29. Chromospheric plasma ejections from along the edge of the LB are indication of magnetic reconnection at the very low altitude, which is close to the height where the vector magnetic fields are measured with SOT. The series of spectro-polarimeter (SP) data shows that highly inclined magnetic field is newly formed along the LB on April 30, although magnetic fields in the LB are in form of lower field strength, more horizontal than in the neighboring umbrae on the both days. The interface between the inclined magnetic field and pre-existing vertically oriented umbral field is exactly located along the chain of the footpoints of chromospheric ejections, suggesting partial reconnection between the magnetic fields with the same direction but obliquely oriented as a key 3-D magnetic field configuration for plasma ejections. In the partial reconnection, only the anti-parallel component of the obliquely oriented magnetic fields can dissipate through reconnection. Moreover, strong vertical electric current higher than 100 mA/m,2 is clearly observed along the interface. We may directly detect electric current sheets in the low-altitude magnetic reconnection with the SP measurement.
Session: Solar Magnetic Activity
Authors: Masumi Shimojo, XRT&SOT/Hinode team
Title: THE RELATIONSHIP BETWEEN THE MAGNETIC FIELD AND THE CORONAL ACTIVITIES IN THE POLAR REGION (Invited Talk)
Abstract: The image of the polar region of the sun is changing based on the observations taken by the three telescopes aboard the Hinode satellite. Based on the data of Solar Optical Telescope (SOT) aboard Hinode, Tsuneta et al. (2008) reported that there are many localized magnetic poles in the polar region, and the magnetic strength of the magnetic poles is over thousand Gauss. They called the strong magnetic pole in the polar region “kG-pathce”. And, Cirtain, et al. (2007) and Savcheva, et al. (2007) presented that the occurrence rate of X-ray jets in the polar region is very high and 10 events/hour. Their result was obtained by the high resolution observations by X-ray Telescope (XRT) aboard Hinode. These results are very important for understanding the fast solar wind that blows from the polar region. On the other hand, in order to understand the activities in the polar region, it is very important to investigate the relationship between the magnetic environments and the coronal structures/activities. In the paper, for the purpose, we aligned the photospheric images (G-band, Stoke-IQUV of FeI), the chromospheric images (Ca II H line, Stokes-V of Na) and coronal images (X-ray) obtained by Hinode, and investigate the relationship. Basically, the co-alignment process was done based on the alignment information of the telescopes reported by Shimizu et al. (2007). And, we aligned the images using the curve of the solar limb, finally. As the result of the co-alignments, we found the following things. 1) On most kG-patches in the polar coronal hole, there is any coronal structure. 2) X-ray jets in the polar coronal hole are not always associated with the kG-patches. Some X-ray jets are associated with very weak magnetic field. And, the jets are strongly associated with the emerging/cancelling magnetic flux. The first one suggests that the coronal heating is not effective only in the magnetic field strong, such as the center of the sunspot. The second result indicates that the producing mechanism of the X-ray jets in the coronal hole is same as that in the other region. And the result suggests that the magnetic activities are not weak even in the coronal hole.
Session: Solar Magnetic Activity
Authors: Siverskyi t. and Zharkova V.V.
Title: The effect of collective electric fields on particle acceleration in a 3D reconnecting current sheet
Abstract: We investigate particle acceleration in 3D reconnecting current sheets with the PIC and test particle approaches for different magnetic field topologies relevant to solar flares and magnetosphere. Particle trajectories, energy spectra and densities are investigated by taking into account the ambient plasma feedback via induction of polarization and turbulent electric fields. Possible implications to diagnostics of acceleration scenarios from observed parameters are discussed.
Session: Flare Physics
AUTHORS:Joan T. Schmelz
Title: Coronal Loop Temperatures Obtained with Hinode XRT: A Toothpaste-Tube Analogy
Abstract: Multi-filter data observed by the Hinode X-Ray Telescope on 10 and 13 July 2007 were used to investigate the thermal properties of coronal loops. At several positions along the loops, differential emission measure analysis revealed a strong peak at Log T = 6.1 (which would predict the presence of a TRACE loop) and a much weaker hot component (which we speculated might be a nanoflare signature). TRACE observations, however, did not reveal the predicted loop, so we were forced to re-examine our assumptions. Good differential emission measure results require high- and low-temperature constraints, but our data sets did not contain images from the thinnest and thickest filters, which would be most likely to provide these constraints. Since differential emission measure programs aim to match observed intensities and get low values of χ2, they may place emission measure in high- and low-temperature bins where it does not belong. We draw an analogy to squeezing the toothpaste tu be in the middle. Our analysis was repeated for a loop observed on 13 May 2007 when the instrument acquired data in 11 filters and filter combinations, including both the thinnest and thickest filters. These results show that the loop is multi-thermal, with significant emission measure in the range 6.0 < Log T < 6.5, but this outcome is dependent on the instrument calibration. The final answer related to the isothermal or multi-thermal nature of these loops will have to wait until the calibration studies are complete.
Session: Perspectives on the Physics of Coronal Loops
AUTHORS:B.Schmieder (Observatoire de Paris, LESIA, F-92195, Meudon Cedex, France) P.Schwartz, P.Heinzel, F.Farnik, S.Gunar (Astronomical Institute, 251 65 Ondrejov, Czech Republic) L.Golub (Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA)
Title: PROMINENCE AND ITS CORONAL CAVITY OBSERVED BY TRACE, HINODE AND SOHO.
Abstract: A prominence is a filament observed at the limb. Filament lies over the inversion line of the photospheric longitudinal magnetic field and is supported in dips of the horizontal magnetic field lines. Recent models of flux tubes prove that fine structures of prominences could be represented by vertical structures embedded in dips of horizontal fieldlines. Observations of a prominence observed in H-alpha by Hinode/SOT and the solar tower in Meudon show a very high dynamic nature. SUMER spectra in Lyman series show no reverse profiles indicating a large prominence coronal transition region. This prominence is surrounded by a large coronal cavity as data from TRACE and Hinode/XRT show. These results suggest presence of many threads along the line-of-sight or/and presence of horizontal structures.
Session: Solar Magnetic Activity
Authors: : Frans Snik, Catherine Fischer, Christoph Keller, Kiyoshi Ichimoto, Alfred de Wijn, Bruce Lites
Title: Observations of scattering polarization at high spatial resolution
Abstract: Weak quiet sun magnetic fields with turbulent topologies are still virtually unobserved, because the Zeeman effect is insensitive to them. The most promising diagnostic of these fields is through the Hanle effect acting on the scattering polarization signals in suitable spectral lines. Because of the low degrees of polarization to be measured, observations of scattering polarization with high spatial resolution are challenging. However, such observations are crucial to map turbulent magnetic fields at the granular scale and study possible local dynamo action by the granulation.
We present Hinode filtergram observations of scattering polarization in the CN band at 388 nm and in the Na I D1 line (core and wings). After eliminating spurious polarization signals due to instrumental polarization and residual image motion and solar evolution during polarization modulation, we perform a statistical analysis of scattering polarization signals from granules and intergranules in quiet sun regions. We discuss the spatial variation of the scattering polarization in the D1 core, which origin is still unknown.
Session: Solar Magnetic Activity
Authors: : Daniel Spicer
Title: Can Reconnection Directly Produce the Requisite Electron Fluxes needed to Explain the Hard X-ray Bursts that Characterize Flares and CMES? (Invited Talk)
Abstract: The orthodox model of a solar flare and CME is that of a single current sheet which reconnects at an X-point. The earliest model of this type was due to Kopp and Pneuman(1976). A common assumption of this class of models is that the electric field produced by the X-point reconnection directly accelerates the requisite electron fluxes (~10**36 20 KeV electrons/s) needed to explain the hard X-ray bursts that characterize flares and CMEs. However, is it easy to demonstrate that this assumption is false, which will be shown during the talk. Nevertheless, image data is consistent with the orthodox model so how does one explain the needed fluxes in the context of the orthodox model? A number of possibilities exist (Spicer etc 2006) that can be tested and each will be briefly discussed.
Kopp, R.A., and G.W. Pneuman (1976), Magnetic Reconnection in the Corona and the Loop Prominence Phenomenon, Solar Physics, 50, 85-98.
D.S.Spicer, D. Sibeck, B.J. Thompson, and J.M. Davila (2006),A Kopp-Pneuman-like Picture of Coronal Mass Ejections, Ap.J. 643, 1304-1316
Session: Flare Physics
Author: : Robert Stein
Title: Supergranulation Solar Convection Simulations
Abstract: Supergranulation scale solar convection simulations (96 Mm wide by 20 Mm deep) have been carried out for 20 hours. This domain encompases only 10 % of the geometric depth of the convection zone, but half its scale heights. For testing local helioseismic methods, four hour averages of density, temperature, sound speed and all three velocity components at two hour cadence are available from: steinr.pa.msu.edu/bob/96averages.
We find that supergranules are present at the surface as well as large depths, but without a magnetic field there is no enhancement at supergranule scales at the surface. Buoyancy driving is largest near the surface but is significant over the entire domain and is balanced primarily by dissipation. The kinetic energy damping length scale is 4 scale heights. The mixing length (entrainment distance) for mass is 1.8 scale heights. The fractional area of upflows is 2/3 over the entire domain except close to the surface where it is slightly larger. The internal (ionization) energy flux is the largest contributor to the convective flux for tempertures below 40,000 K and the thermal energy flux is the largest contributor at higher temperatures.
This work is supported by NASA grants NNX07AO71G, NNX07AH79G, NNX08AH44G and NSF grant AST0605738. The calculations were performed at the NASA Advanced Supercomputing Division facilities.
Session: Bringing Modeling and Obvservations Together
Author: : Oskar Steiner
Title: The horizontal internetwork magnetic field: numerical simulations in comparison to observations with Hinode
Abstract: Observations with the Hinode space observatory led to the discovery of predominantly horizontal magnetic fields in the photosphere of the quiet internetwork region. In this contribution we investigate realistic numerical simulations of the surface layers of the Sun with respect to the horizontal magnetic fields and compute the corresponding polarimetric response in the Fe I 630 nm line pair. We find a local maximum in the mean strength of the horizontal field component at a height of around 500 km in the photosphere, where, depending on the initial state or the boundary condition, it surpasses the vertical component by a factor of 2.0 or 5.6.
We show and discuss the corresponding response as seen in the synthesized Stokes profiles. We find that convective overshooting is responsible for the expulsion of horizontal fields to the upper photosphere. This renders the Poynting flux positive in the photosphere, whereas it is is negative in the convectively unstable layer below. We estimate its size an possible contribution to ohmic heating.
Session: Bringing Modeling and Obvservations Together
Author: : Sterling, Alphonse C., Harra, Louise K., Moore, Ronald M.
Title: CME-Producing Precursors to the 2006 December 13 X-Flare
Abstract: We revisit one of the largest explosions observed during the Hinode era, the X4.3 class event of 2006 Dec 13. We gain insight into the main eruption through study of two sub-C-class precursor eruptions, occurring within 12 hours of and originating from the same (or nearby) neutral line as the X-flare. The precursors share some features in common with the main eruption, and their lower energy and consequent slower development renders interpretation of these features easier to decipher than in the rapidly explosive main eruption. In addition, because the weak precursors occurred in a magnetically strong region, magnetic connections indicated by soft X-ray loops are readily visible in these cases, while such connections can be much less apparent in weaker-region eruptions. Hinode/SOT magnetograms indicate that photospheric magnetic dynamic activity in the "magnetic core" is the likely ultimate source of the eruptions. All the eruptions, however, produce Coronal Mass Ejections (CMEs) that have wider spatial extent than the localized source region; this is a long-observed but puzzling phenomena, which can address directly here using the high-quality Hinode data. For the precursor eruptions, Hinode/XRT images show that the initial eruptions occur inside larger-scale magnetic structures that encompass the core. The exploding core field blows out this larger-scale structure, resulting in the CME having angular extent far exceeding that of the source-region core alone; this is the arch-arch-blowout scenario for CMEs of Moore & Sterling (2007). Similar processes occur in the main eruption, except that the much larger energy release in that eruption compared to the precursors results in much faster and larger-scale phenomena.
Session: Source of the Solar Wind/CME
Authors: : Yingna Su, Adriaan van Ballegooijen, Bruce W. Lites, Edward E. Deluca, Leon Golub, Paolo Grigis, Guangli Huang, and Haisheng Ji
Title: OBSERVATIONS AND NLFFF MODELING OF ACTIVE REGION 10953
Abstract: We present multi-wavelength observations of a simple bipolar active region (NOAA 10953), which produced several small flares (mostly B class and one C8.5 class) and filament activations from April 30 to May 3 in 2007. We also explore non-linear force free field (NLFFF) modeling of this region prior to the C8.5 flare on May 2, using magnetograph data from SOHO/MDI and Hinode/SOT. A series of NLFFF models are constructed using the flux-rope insertion method. By comparing the model field lines with multiple non-potential X-ray loops observed by Hinode/XRT, we find that the axial flux of the flux rope in the best-fit models is 7e20 Mx, while the poloidal flux has a wider range of (0.1--10)e10 Mx/cm. The axial flux in the best-fit model is well below the upper limit (~15e20 Mx) for eruption, which is consistent with the fact that no successful full filament eruption occurred in this active region. From multi-wavelength observations of the C8.5 flare, we find that the X-ray brightenings (in both RHESSI and XRT) appeared about 20 minutes earlier than the EUV brightenings seen in TRACE 171 images and filament activations seen in MLSO H-alpha images. This is interpreted as indicating that the X-ray emission may be caused by direct coronal heating due to reconnection, and the energy transported to the chromosphere may be too low to produce EUV brightenings. This flare started from nearly unsheared flare loop(s), unlike most two-ribbon flares which begin with highly sheared footpoint brightenings. By comparing with our NLFFF model, we find that the early flare loop is located above the flux rope which has a sharp boundary. We suggest that this flare started near the outer edge of the flux rope, not at the inner side or at the bottom as in the standard two-ribbon flare model.
Session: Flare Physics
Authors: : Y. Suematsu, K. Ichimoto, Y. Katsukawa, S. Tsuneta, T. Shimizu, T. Tarbell and R. Shine
Title: Dynamical Nature of Solar Chromospheric Fine Structures Revealed with HINODE/SOT
Abstract: Major part of the solar chromosphere consists of small-scale jet-like structures called spicules off the limb and mottles or fibrils on the disk. These jet-like structures (hereafter referred to as spicules) are likely to play an important role in maintaining the energy balance of the local atomsphere and the mass balance of the corona. High time and spatial resolution observations in Ca II H, H-alpha and even Na I D line filtergraph of the Solar Optical Telescope (SOT) aboard Hinode have revealed that the spicule consists of highly dynamic multi-threads (typically twin) of as thin as a few tenths of arcseconds and shows prominent lateral movement or oscillation with rotation on its axis during its life. The fine structure and lateral motion imply that the spicules can be ejected by magnetic reconnection at footpoints. Since most spicules emanate from seemingly uni-polar magnetic region and the relevant magnetic reconnection should take place in unresolved spatial scale contrary to the larger-scale jets such as macro-spicules and surges. Here, we summarize the dynamical nature of the chromospheric fine structures revealed with the SOT.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Takeru Suzuki
Title: Alfvenic Energy Supply to the Solar Atmosphere and Wind (Invited Talk)
Abstract: I introduce recent theoretical attempts to connect energy transfer from the photosphere to corona/wind regions by Alfven waves, with referring to HINODE observations of polar magnetic fields (e.g. Tsuneta et al.2008). Up to a few years ago, most people separately modeled photosphere-chromosphere and corona-wind in order to avoid various difficulties at the transition region. Recently, models and simulations covering the entire atmosphere (i.e. from photosphere to wind) are presented (Cranmer et al.2007; Suzuki & Inutsuka 2005;2006). Then, these are tools for quantitative studies of propagation, reflection, and dissipation of Alfven waves which are generated by footpoint motions of flux tubes and transient events. In this talk, I firstly present the results of these theoretical works. Then, I discuss transmittancy of Alfven waves into coronal regions through transition region in terms of the geometries of magnetic flux tubes.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: : Martínez-Sykora, J.; Hansteen, V; Carlsson Mats
Title: 3D Magnetic flux emergence simulations from the convection zone to the corona.
Abstract: We have carried out 3D numerical simulations of magnetic flux tube emergence in a computational domain spanning the upper layers of the convection zone to the lower corona. We use the Oslo Stagger Code (OSC) to solve the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along the agnetic field lines. The response of the photosphere, chromosphere and pre-existing magnetic field to the rising flux tube is described with magnetic intensities, synthetic continuum images at different wavelengths, as well as synthetic Ca II H-line images and velocity field distributions. We will describe the emergence of a magnetic flux tube into such an atmosphere and we will show the different diagnostic to compare with the observations.
Session: Bringing Modeling and Obvservations Together
Authors: : Luca Teriaca
Title: Results from the Hinode/SUMER Campaign
Abstract: The SUMER VUV spectrometer aboard SOHO currently observes spectral lines and continua in the 67 nm to 150 nm range. This emission mostly samples the solar atmosphere from the chromosphere to the lower corona (<= 1 MK), through the transition region. As such, this instrument is an ideal complement to the Hinode instruments, helping coupling the observations of the photospheric magnetic field and of the photospheric and chromospheric emission performed by SOT with the images and spectra of the hot corona (>= 1 MK) obtained by XRT and EIS. Since the launch of Hinode at the end of 2006, there have been five SUMER campaigns during which combined observations were obtained. Of these, three are full bilateral joint campaigns, the last of which is running at the time of this meeting. Here I report on some of the scientific results derived from these campaigns.
Session: Past, Present, and Future Collaborative Observational/Theory
Author: : Jaume Terradas
Title: Resonant absorption in complicated plasma configurations: applications to multi-stranded coronal loop oscillations
Abstract: We study the excitation and damping of transverse oscillations in a multi-stranded model of a straight line-tied coronal loop. The transverse geometry of our equilibrium configuration is quite irregular and more realistic than the usual cylindrical loop model. By numerically solving the time-dependent ideal magnetohydrodynamic equations in two dimensions we show how the global motion of the whole bundle of strands, excited by an external disturbance, is converted into localized Alfv\'enic motions due to the process of resonant absorption. This process produces the attenuation of the transverse oscillations. We find that the mechanism of mode conversion is not compromised by the complicated geometry of the model. The extension of this work to a full three-dimensional nonlinear model is also discussed.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: Paola Testa, Fabio Reale, Ed DeLuca
Title: Investigating Hot Temperature Emission from Non-Flaring Active Regions
Abstract: We present a study of the thermal properties of coronal plasma in non-flaring active regions using simultaneous Hinode XRT and EIS observations. The multi-filter (7 filters) XRT dataset together with EIS spectra including its entire wavelength range allow to accurately determine the thermal structure of the X-ray emitting active region plasma, and to explore the presence of hot plasma (T ~ 10MK) in non-flaring regions. We will discuss our preliminary results also in the context of coronal heating models.
Session: Perspectives on the Physics of Coronal Loops
Authors: H. Tian
Title: Cool and hot components of a coronal bright point
Abstract: We performed a systematic study of the Doppler shifts and electron density measured in an EUV bright point observed simultaneously in more than 10 EUV lines with formation temperatures from log(T/K) = 4.5 to 6.3. Those parts of a BP seen in transition region and coronal lines are de¯ned as its cool and hot components, respectively. We find that the transition from cool to hot occurs at a temperature around log(T/K) = 5.6+-0.1. The two components of the BP reveal a totally different orientation and Doppler-shift pattern, which might result from a twist of the associated magnetic loop system. The analysis of magnetic-field evolution and topology seems to favour a two-stage heating process, in which magnetic cancelation and separator reconnection are powering, respectively, the cool and hot components of the BP. We also found that the electron densities of both the cool and hot components of the BP are higher than those of the surrounding quiet Sun, and comparable to or smaller than active-region densities.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: : Alan Title
Title: Ponds, Fragments, and the Distribution of the Surface Magnetic Field
Abstract: Recent controversy about the large number of apparently unpaired magnetic fragments compared to bipolar emergence is now clearer with recent numerical simulations of flux emergence. Much magnetic field apparently emerges from an oval shaped flatten “pond” immediately below the surface. The strong downflows in the surface convection distorts the emerging flux into a complex see of bipoles that are not easily recognized as pairs because of the complexity of the emergence process.
Session: Bringing Modeling and Obvservations Together
Authors: : Steve Tomczyk
Title: Alfven Waves in the Corona
Abstract: Recent velocity imaging observations obtained with the Coronal Multi-channel Polarimeter (CoMP) instrument reveal the existence of ubiquitous propagating Alfvén waves in the solar corona. These data present an exciting opportunity for probing the structure and magnetic topology of the coronal plasma through coronal seismology. We present the results of a detailed analysis of Alfven wave observations which allow the determination of the phase speed of the waves and the relative quantity of outward and inward wave flux. This analysis also provides a k-omega diagnostic diagram of coronal waves. We discuss current and future prospects for coronal seismology with these data.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: H. Tonooka, M. Shimojo (NAOJ), N. Tokimasa (NHAO), K. Yaji (Rikkyo Univ.) and PAONET Working Group for Public Use of Hinode Data
Title: Hinode DVD for public outreach
Abstract: Hinode Science Center of NAOJ and PAONET Working Group for Public Use of Hinode Data published a DVD introducing the background and the initial observations of Hinode for public outreach. The DVD was released on March 2008 for Japanese version, and will be released on September 2008 for English version. This was aimed at interpreters/educators of science, i.e. a science museum person or a science teacher. The English version of the DVD contains two video programs, the 3 minutes short version and the 16 minutes long version, both of which can be played on a DVD player, Full HD version of the video programs are also available in DVD-ROM, demonstrating the excellence of large format detectors of Hinode, which can be played on SONY PlayStation3(TM). We will show the highlights of the DVD on the poster. Furthermore just pressed English version DVD will be distributed at the meeting.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: : D. Tripathi, H.E. Mason, B.N. Dwivedi, G. Del Zanna, P.R. Ypung
Title: Solar Active Region Loops: Hinode/EIS observation
Abstract: We have carried out a study of active region loops using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode. An active region was observed using 1 arcsec slit on May 19, 2007. We find that active region structures which are clearly discernible in cooler lines (1MK) become 'fuzzy' at higher temperatures (2MK). The active region was comprised of red- shifted emissions (downflows) in the core and blue-shifted emissions (upflows) at the boundary. The flow velocities estimated in two regions located near the foot points of coronal loop showed red-shifted emission at transition region temperature and blue shifted emission at coronal temperature. The outflow speed in these regions increased with temperature. For more detailed study we selected one particular well defined loop. Downward flows are detected along the coronal loop, being higher in lower temperature lines (rising up to 60 km/s near the foot point). The downflow was localized towards the footpoint in transition region lines Mg VII and towards the loop top in high temperature line Fe XV. By carefully accounting for the background emission we found that the loop structure was close to isothermal for each position along the loop, with the temperature rising from around 1 MK to 1.5 MK from the close to the base to higher up towards the apex (~75 Mm). We derived electron density using well established line ratio diagnostic techniques. Electron densities along the active region loop were found to vary from 10^10 cm^-3 close to the footpoint to 108.5 cm^-3 higher up. A lower electron density, varying from 10^9 cm^-3 close to the footpoint to 10^8.5 cm-3 higher up, was found for the lower temperature density diagnostic. Using these densities we derived filling factors in along the coronal loop which can be as low as 0.02 near the base of the loop. The filling factor increased with projected height of the loop. This study provides important constraints on loop modeling.
Session: Perspectives on the Physics of Coronal Loops
Authors: : D. Tripathi, S.E. Gibson, J. Qiu, L. Fletcher, R. Liu, H. Gilbert, H.E. Mason
Title: Partial eruption of prominences: Observations and comparison with model predicted observables
Abstract: We have investigated several partially erupting prominences to study their relationship with other CME associated phenomena and to compare these observations with observables predicted by the model of partially erupting flux ropes by Gibson \& Fan (2006a,c). For this purpose we have used multi wavelength observations recorded by the Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO) and soft X-ray telescope (SXT). The observational features associated with partially erupting prominences were then compared with the predicted observables by the model. The observables predicted by the partial eruption model are well observed in association with partially erupting prominences. The partial eruption model provides a viable mechanism to explain most of the observational phenomena associated with a CME eruption related with a partially erupting prominence.
Session: Bringing Modeling and Obvservations Together
Authors: Alexandra Tritschler
Title: Sunspot Structure and Dynamics (Keynote Talk)
Abstract: The physics of Sunspots is a fascinating and demanding field of research in solar astronomy. The interaction of magnetic fields and plasma flows takes place in a tangled magnetic geometry and occurs on spatial scales that pose a continuous challenge for existing instrumentation and for the unambiguous interpretation of spectropolarimetric observations. Thus, the main properties of sunspots are well established but its fine structure is not yet fully understood (and characterized).
In this presentation I summarize the current knowledge of the magnetic and dynamic properties of sunspots at the photospheric level based on selected observations featuring the highest possible spatial and spectral resolution. The review will concentrate on light bridges, umbral dots, penumbral filaments and the notorious dark cores. I will discuss the morphology of the fine structure elements but mostly focus on observed intensities, line-of-sight velocities, proper motions, magnetic field parameters and the net-circular polarization.
With the launch of HINODE a stable window to the Sun opened, providing a spatial resolution close to the diffraction limit of its telescope. Hence, the joint effort of ground-based and space-borne observations should lead to substantial progress in characterization of the various small-scale inhomogeneities observed in sunspots.
Session: Sunspot Structure and Dynamics
Authors: Javier Trujillo Bueno
Title: Some Suggestions to "See" the Hidden Magnetism of the Solar Atmosphere (Invited Talk)
Abstract: Solar magnetic fields leave their fingerprints on the polarization signatures of the emergent spectral line radiation. This occurs through a variety of rather unfamiliar physical mechanisms, not only via the Zeeman effect. In particular, magnetic fields modify the atomic level polarization (population imbalances and quantum coherences) that anisotropic radiative pumping processes induce in the atoms and molecules of the solar atmosphere. Interestingly, this so-called Hanle effect allows us to "see" magnetic fields to which the Zeeman effect is blind within the limitations of the available instrumentation (e.g., a recent Hanle-effect investigation showed that the bulk of the solar photosphere appears to be filled with tangled fields at subresolution scales, of order 100 G, which may be important for the overall energy balance of the solar atmosphere). In this talk I will show some of the remarkable signatures that the atomic level polarization produces on the emergent spectral line radiation, arguing that the observation and modeling of such polarization effects might lead to a true revolution in our empirical understanding of chromospheric and coronal magnetism. To this end, it is crucial that the design of any future solar telescope (e.g., ATST, EST or SOLAR-C) incorporates the scientific case of the spectral line polarization produced by the joint action of the Hanle and Zeeman effects.
Session: Solar magnetic Activity
Authors: Saku Tsuneta
Title: Is the polar region different from the quiet Sun? (Invited Talk)
Abstract: We present the magnetic landscape of the polar region of the Sun as observed with Hinode (Tsuneta et al 2008). We found many vertically-oriented magnetic flux tubes with field strength as strong as 1 kG that are scattered in the whole polar region. They all have the same polarity. The polar region is also covered with ubiquitous horizontal fields. The PDF (probability distribution function) for field strength of the horizontal magnetic field is remarkably similar to that of the quiet sun and an active region as obtained by Ishikawa and Tsuneta (2008). PDF for the vertical field is exactly the same as that for the quiet sun. Uni-polarity of the polar region differentiates it from the quiet Sun. Difference and similarity between the quiet sun and the polar regions are summarized (Itoh and Tsuneta, 2008), and its implication for the solar wind acceleration will be discussed.
Session: Solar magnetic Activity
Authors: Turkmani, R., Brown, J., Kontar, E.
Title: Local reacceleration of electrons by current sheet cascade in the dense chromosphere
Abstract: Current sheets cascades (CSCs) in the dense chromosphere are suggested as a candidate mechanism for local reacceleration of electrons. Such Local Reacceleration Models (LRMs) may offer an alternative to the 'standard' collisional thick target injection model (TTM) (Brown 1971) of solar hard X-ray (HXR) burst sources, requiring far fewer electrons and solving some recent problems with the TTM interpretation.
In LRMs electrons are locally confined and continuously re-accelerated, with lifetimes much longer than collisional, radiating HXRs throughout reacceleration volume V.
Results from combined 3D MHD/test particle simulations suggest that CSCs in the dense chromosphere can yield a high enough non-thermal emission measure for large HXR events.
Recent results from HINODE (Abramenko et al 2008) shows the high complexity of photospheric fields preceding increased complexity in the corona followed by a flare. Such observations support the idea of current sheets present in the photospher which could lead to electrons accelerated and re-accelerated locally in the photosphere.
Session: Flare Physics
Authors: I. Ugarte-Urra, H.P. Warren, D.H. Brooks & A. Degiorgi
Title: Hinode Coronal Loop Observations (Invited Talk)
Abstract: The relationship between loop structures at various temperatures in the solar corona is still under investigation. Loops with temperatures above 3MK have been traditionally considered steady and independent from the evolution of cooler loop structures seen in the corona. The EUV Imaging Spectrometer (EIS) on board Hinode provides monochromatic imaging at an unprecedented cadence and temperature coverage. Recent simultaneous and uninterrupted EIS and XRT observations indicate that there is a significant population of loops that undergo a heating and cooling process that makes them reach temperatures above 3 MK and slowly cool through all the temperatures down to the transition region. This result establishes a direct link between the structures formed at all of the dominant temperatures in the atmosphere.
Session: Perspectives on the Physics of Coronal Loops
Authors: M. Velli
Title: Sources of the Solar Wind.(Keynote Talk)
Abstract: The Ulysses spacecraft, presently terminating its mission, has conclusively demonstrated that the solar wind, at solar minimum, has a well defined bi-modal structure, with the prevailing source of the high speed streams located within coronal holes, and the slow solar wind apparently confined to the magnetic activity belt, possibly escaping from previously closed coronal magnetic regions. Alternatively, the source of the slow wind could be the rapidly expanding magnetic field regions at the coronal hole boundary.
In this talk I will rapidly review our present knowledge of the source regions of the solar wind throughout the activity cycle, then discuss what coronal heating and acceleration mechanisms might be prevalent in each, to conclude with which observations from current and future experiments might be crucial in disproving or discriminating among the panoply of models - from Alfven waves, high frequency cyclotron modes and MHD turbulence to shocks and magnetic reconnection between closed and open fields - developed since Parker's original prediction of the solar wind outflow 50 years ago.
Session: Perspectives on the Physics of Coronal Loops
Authors: Alison Wallace, Louise Harra, Alphonse Sterling & Suguru Kamio
Title: The Life-cycle of a small flare – how a small loop can cause large-scale disruption.
Abstract: We examine the life-cycle of a small B-Class flare that took place at 13:38 UT on May 12, 2007. Starting 24hrs before the flare, flux emerges at the Western edge of the region. Analysis of the pre-flare Hinode observations show small-scale brightenings and plasma flows at the interaction site of the emerging flux and preexisting field. During the main phase of the flare loop expansion takes place at a velocity of around 20km/s, which stops after 34min. The lack of a CME in LASCO and COR2 in STEREO indicate that the event remains confined, however, this does not prevent its effects being observed away from the flaring active region. First there is brightening in a nearby bipole which is connected to the active region via a large coronal loop observed in STEREO 195A data. A dimming is also seen moving in a Westward direction with a slow speed of a few km/s and is first observed 90min after the flare and 1.3x10^5km from the core of the active region. We believe that these events are directly connected to the flare and will present our analysis to show that the small-scale interactions, which initially triggered the flare in this active region, can be responsible for large-scale effects even for confined events.
Session: Flare Physics
Authors: R.W.Walsh, J.B. Noglik, R.C. Maclean
Title: Deconstructing AR10961: a multi-instrument examination using Hinode, STEREO, TRACE & SOHO
Abstract: Active region 10961 was observed over a five day period (2007 July 2-6) by instrumentation on-board Hinode, STEREO, TRACE and SOHO. As it progressed from Sun centre to the solar limb a comprehensive analysis of the EUV, X-ray and magnetic field data reveals clearly observable changes in the global nature of the region. Temperature analyses undertaken using STEREO EUVI double filter ratios and XRT single and combined filter ratios demonstrate an overall cooling of the region from between 1.6 - 3.0 MK to 1.0 - 2.0 MK over the five days. Similarly, Hinode EIS density measurements show a corresponding increase in density of 27%. Moss, cool (1 MK) outer loop areas and hotter core loop regions were examined and compared with potential magnetic field extrapolations from SOHO MDI magnetogram data. In particular it was found that the potential field model was able to predict the structure of the hotter X-ray loops and that the larger cool loops seen in 171 Angstrom images appeared to follow the separatrix surfaces. The reasons behind the high density moss regions only observed on one side of the active region are examined further.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Authors: R.W. Walsh and M. Marsh
Title: Towards 3D coronal seismology- multi-vantage point observations of slow magnetoacoustic waves
Abstract: On 2008 January 10, the twin Solar Terrestrial Relations Observatory A and B spacecraft conducted a high time cadence study of the solar corona with the Extreme UltraViolet Imager instruments to investigate coronal dynamics. Coupled with context images from the Sun-earth line from Hinode, observations of the three-dimensional propagation of waves within active region coronal loops are obtained for the first time. Intensity oscillations with a range of periodicities were detected propagating outwards from the base of a loop system with the dominant power residing in an ~ 12 minute oscillatory signal. A novel analysis technique was applied to measure the wave phase velocity in the multi-vantage point observations. This stereoscopic view was employed to infer the three-dimensional velocity vector of the wave propagation. Although it is calculated from B that the wave speed is 62 km/s, when observed from A, the value estimated rises to 104 km/s. It was found that an inclination of the loop structure of 36.8 degrees to the local normal provides a true wave velocity of magnitude 132 km/s in both cases.
Session: Perspectives on the Physics of Coronal Loops
Authors: T.J. Wang and L. Ofman
Title: Propagating slow acoustic waves in coronal loops observed by Hinode/EIS
Abstract: We report Hinode/EIS observations of quasi-periodic Doppler shift oscillations near the footpoint of a coronal loop. The observations were made with the 1" slit in a sit-and-stare spectroscopy mode. The oscillations are detected simultaneously in several EUV lines such as in Fe XII, Fe XIII, Fe XIV and Fe XV, but most evident in Fe XII 195\AA. These oscillations are nonflare related and are presented thorough the whole period of the observation for a tracked target (over two days), characterized by a train of scillations with a more or less constant period on the order of 5 min and an amplitude on the order of 1 km/s. It can be excluded that these oscillations are due to jitters of the spacecraft pointing by modeling the observation based on a preceding raster image and spacecraft drifts determined from the housekeeping data. In some oscillation trains, the associated intensity oscillations are observed in phase with the Doppler shift oscillation, indicative of the signature of the propagating slow acoustic waves. These waves could be caused by the leakage of 5 min photospheric p-modes into the coronal structure, as suggested by the previous studies on TRACE EUV observations of the propagating waves in long fan-like coronal structure. However, here we find the waves existing in a short and relatively hot coronal loop.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: T. J. Wang, L. Sui, J. Qiu
Title: Direct observation Of high-speed reconnection outflows with SOHO/SUMER, TRACE and RHESSI
Abstract: Spectroscopic observations of a solar limb flare recorded by SUMER on SOHO reveal, for the first time, hot fast magnetic reconnection outflows in the corona. The Observations from TRACE and RHESSI allow us to determine the location of magnetic reconnection region. We find that as the reconnection site rises across the SUMER spectrometer slit, significant blue- and red-shift signatures are observed in the Fe XIX line, reflecting upflows and downflows of hot plasma jets, respectively. With the projection effect corrected, the measured outflow speed is between about 900-3500 km/s, consistent with thoeretic predictions. Based on theoretic models, the magnetic field strength near the reconnection region is estimated to be 19-37 Gauss. Our observations of reconnection jets and other signatures such as the erupting flux loop and cusp-shaped postflare loops are consistent with the classic scenario of magnetic reconnection of solar flares. In addition, I will discuss the importance of this study in guiding the future Hinode/EIS and XRT observations.
Session: Flare Physics
Authors: : Tetsuya Watanabe, Hirohisa Hara, Alphonse C. Sterling, and Louise K. Harra
Title: Production of high-temperature plasmas at the initial phase of a C9.7 flare
Abstract: The EIS study (#35): HH_AR+FLR_RAS_H01 enables a high-cadence raster scanning observation for an area of 240 arcsec x 240 arcsec, with 1 arcsec slit skipping E-W 10 arcsecs every time. The exposure time per slit position is set to 5 seconds, and the time cadence of the entire area is about 160 seconds. This study have caught the initial phase of a C9.7 flare occurred on June 6, 2007.
A raster image taken during 17:20:09 - 17:20:29 show a few bright patches of FeXXIII/FeXXIV emission lines at the footpoints of flaring loops, which are not clearly seen in the image taken at 17:17:30 - 17:17:49. FeXXIII spectra at these footpoints present completely blue-shifted components of 300 - 400 km/s, while FeXV/VIV lines are nearly stationary, the FeXII lines and/or lower-temperature lines show slightly red-shifted features, and the SiVII line presents a ~60km/s red-shifted component. Density of 1.5 - 2 MK plasma at these foot points are estimated to 3 x 1010 cm-3 by FeXIII/XIV line pairs.
High-temperature loops connecting the above-noted footpoints emerge in the FeXXIII/FeXXIV images taken during 17:22:49 - 17:23:08. Line profiles of these high-temperature lines taken at the flare peak show only stationary components. Relatively weak FeXVII line at 254.8A reveals predominance of high-temperature plasma (> 107 K) in these loops.
Session: Flare Physics
Authors: Harry Warren, Ignacio Ugarte-Urra, Amanda Degiorgi
Title: The Temperature Structure of Active Region Loops
Abstract: Previous solar observations have shown that coronal loops near 1 MK are difficult to reconcile with simple heating models. These loops have lifetimes that are long relative to a radiative cooling time and densities that are large relative to thermodynamic equilibrium. Models proposed to explain these properties generally rely on the existence of small scale filaments that are in various stages of heating and cooling, suggesting a distribution of temperatures within a loop. We present the differential emission measure analysis of coronal loops observed with EIS. We find that coronal loops that are bright in Fe XII have narrow temperature distributions, but are not isothermal. We also derive volumetric filling factors in these loops of approximately 10%. Comparisons with TRACE, EUVI, and XRT observations indicate that these loops are evolving.
Session: Perspectives on the Physics of Coronal Loops
Authors: : H. Watanabe, R. Kitai, K. Ichimoto, Y. Katsukawa
Title: Magnetic Structure of Umbral Dots with SOT SP
Abstract: High resolution and seeing-free spectroscopic observation of a decaying sunspot was done with SOT spectro-polarimeter (SP). We report about magnetic structures and Doppler velocity fields around umbral dots (UDs) based on the Milne-Eddington inversion to Fe I 630.2nm full Stokes profiles. As a result, a center-to-limb variation was detected in their magnetic field strength, inclination angle, and Doppler velocity. Observed at disk center, UDs have (i)smaller field strength (-37 Gauss), (ii)more horizontal field inclination (0.9degree), and (iii)locally upward velocity (51 m/s) compared to their surroundings. When the sunspot got close to the limb, UDs and their surroundings showed almost no difference in the magnetic and Doppler values. This center-to-limb variation can be understood by the formation height distribution in a cusp-shaped magnetized atmosphere around UDs due to field-free hot gas intrusion. In addition, we will report our new finding of repetitive UD brightening at spatially localized points with about 15min periodicity.
Session: Sunspot Structure and Dynamics
Authors: M. Weber
Title: Characterizing the Temperature Discrimination Capability of the X-Ray Telescope
Abstract: The Hinode X-Ray Telescope (XRT) has 9 focal-plane filters with different broadband responses. These permit temperature analysis of coronal plasmas with DEM techniques (differential emission measure). Imagers like XRT can achieve larger fields of view and faster cadence than spectrographs, so they enable useful and complementary analyses. Part of DEM analysis involves partitioning the observable temperature range, which is traditionally done with uniform bins in log T. Using the method of Singular Value Decomposition (SVD), we present an analysis to characterize the temperature discrimination abilities of the XRT across the effective temperature range of the filter set. We explore how XRT's temperature diagnostic capability is uneven across the useful temperature range. This information will be useful in designing thermal studies to increase the robustness of the temperature solutions and to optimize the information content.
Session: Hinode Perspectives on Coronal/Chromoshperic Heating
Authors: D.R. Williams and D.H. Brooks
Title: The density stratification in active region cool loops observed at the solar limb
Abstract: Hinode EIS has a unique combination of sensitivity, spatial and spectral resolution that allows unprecedented temperature fidelity and density diagnostic precision. EIS thus reveals in new detail the structural composition of solar active regions as a function of temperature. Images formed by line-integrating slit-scan data of EIS transition region lines, show clear extended peripheral cool loops extending to great heights, rather like those seen with TRACE in hotter coronal lines. Other work presented at this meeting (Ugarte Urra et al.) indicates that these peripheral cool loops represent a different class than the compact, multi-temperature cooling loops in the core of an active region. Furthermore, at transition region temperatures these are the most obvious active region structures, and the regions in which these loops are formed have recently been implicated as possible sources of the slow solar wind.
In this paper we analyse Mg VII density maps of AR 10978 and examine the density stratification of these features above the solar limb. We find that the electron density scale height is shorter in these structures than that measured in the quiet Sun by previous instrumentation. The electron density, however, remains higher than in the quiet Sun, even at the point where they are no longer observable. This is because the emission measure becomes comparable to that of the ambient quiet Sun and makes it difficult to measure their full extent, despite the fact that the density measurements suggest that they persist much higher.
Session: Perspectives on the Physics of Coronal Loops
Authors: Henry Winter, Petrus Martens
Title: Simulating Flares in XRT
Abstract: We simulate a series of flares using the HyLoop code. HyLoop combines the effects of a hydrodynamic, thermal plasma and high-energy, nonthermal particles in a self-consistent model that uses the nonthermal particle collisions as momentum and energy inputs to the thermal model and the thermal plasma as an evolving target for the nonthermal particles. The nonthermal particles for each flare are drawn from different probability distributions in energy and pitch-angle. Accurate simulations of XRT filter responses and hard X-ray emission in multiple passbands are made for each flare and error statistics provided. The simulated emission is analyzed for signatures that can be reliably used as discriminators for nonthermal particle injection mechanisms.
Session: Bringing Modeling and Obvservations Together
Authors: Friedrich Woeger, Sven Wedemeyer-Boehm, Thomas Rimmele
Title: Morphology and dynamics of photospheric and chromospheric magnetic fields
Abstract: We use joint observations obtained with the Hinode space observatory and the Interferometric Bidimensional Spectrometer (IBIS) installed at the DST of the NSO/SP to investigate the morphology and dynamics of magnetic fields in the photosphere and their counterparts in the chromosphere. In this contribution we will explain some of the difficulties in deriving the magnetic field vector from observations of the chromosphere, and present results of the analysis of our observations. In weak field regions we find structures similar to those seen in numerical simulations by Wedemeyer et al. (2004). The weak magnetic flux elements in the chromospheric network are stable and seem to resemble the spatially extended counterparts to the underlying photospheric magnetic elements. In inter-network regions we find no significant flux contributions above the detection limit of IBIS.
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: : T. Yokoyama & H. Isobe
Title: Temporal evolution of a Current Sheet with Initial Finite Perturbationsby Three-dimensional MHD Simulations
Abstract: Temporal evolution of a current sheet with initial perturbations is studied by using the three-dimensional resistive magnetohydrodynamic (MHD) simulations.
The magnetic reconnection is considered to be the main engine of the energy release in solar flares. The structure of the diffusion region is, however, not still understood under the circumstances with enormously large magnetic Reynolds number as the solar corona.
In particular, the relationship between the flare's macroscopic physics and the microscopic ones are unclear. It is generally believed that the MHD turbulence should play a role in the intermediate scale.
The initial current sheet is in an approximately hydromagnetic equilibrium with anti-parallel magnetic field in the y-direction. We imposed a finite-amplitude perturbations (=50%) on the resistivity with a random spatial distribution and see what happens. Special attention is paid upon the evolution of a three-dimensional structure in the direction along the initial electric current (z-direction). Our preliminary results are as follows: (1) In the early phase of the evolution, high wavenumber modes in the z-direction are excited and grow. The energy spectrum in the later stage approaches a power-law function. It indicates a turbulent nature of the system. (2) Many "X"-type neutral points (lines) are generated along the magnetic neutral line (plane) in the current sheet. When they evolve into the non-linear phase, three-dimensional structures in the z-direction also evolve. The spatial scale in the z-direction seems to be almost comparable with that in the xy-plane. (3) The energy release rate is reduced in case of 3D simulations compared with 2D ones probably because of the reduction of the inflow cross sections by the formation of pattchy structures in the current sheet.
Session: Flare Physics
Authors: : Y. Mimura, T. Yokoyama & H. Isobe
Title: Three-dimensional MHD simulations of a damping oscillation in a straight magnetic tube
Abstract: The oscillations of coronal loops can be used as a diagnostic tool for the coronal variables including the local magnetic strength. Recent observations suggest that such oscillations are subject to a rapid damping within several oscillation periods. It is important to make the physical mechanism of the damping clear since it is probably a key for understanding the coronal heating. In order to study this, we performed three-dimensional MHD simulations of oscillations of a straight tube. The resonant absorption around the edges of the tube is effective as a damping mechanism. Moreover we discovered that the Rayleigh-Taylor instability occurs in the vicinity of the center of the loop. The role of this instability will be discussed.
Session: Hinode Perspectives on Coronal/Chromospheric Heating
Authors: N. Yamamoto*, T. Watanabe1, H. A. Sakaue2, N. Nakamura3, E. Watanabe3, N. Tamura2, K. Sato2, H. Funaba2, C. Suzuki2, I. Murakami2, D. Kato2, and T. Kato2
* Institute of Laser Engineering, Osaka University
1) National Astronomical Observatory of Japan
2) National Institute for Fusion Science
3) The University of Electro-Communications
Title: Evaluation of density sensitive line intensity ratios on Fe X-XIII with measured spectra by HINODE, LHD and compact-EBIT
Abstract: On board HINODE (Solar-B) satellite, high-precision spectrometer EIS (EUV imaging spectrometer) have been equipped, which observes in the EUV wavelengths of 170-210A and 250-290A. In the EIS shorter wavelength band between 170A and 210A, many Fe VIII-XIII lines from solar plasmas in the transition region and corona are observed, and spectral lines of these ions can be used to diagnose electron densities of solar plasmas. Therefore, the validity of theoretical models for density diagnostics is crucial in the solar case, and it should be evaluated by parameter-controlled laboratory plasmas. Plasmas produced by the Large Helical Device (LHD) and a compact Electron Beam Ion Trap (EBIT) are adopted as sample laboratory plasmas in this study. Two theoretical models are evaluated; the CHIANTI code (Dere et al. 1997) and our original model accommodating the most recent atomic data calculated by R-matrix method that takes relativistic theory into account [e.g. Aggarwal & Keenan (2005) for Fe XIII]. Spectra generated by these theoretical models are compared with those observed by HINODE, and those produced by LHD and the compact-EBIT. Especially, density sensitive ratios of Fe XIII line intensities are evaluated in detail (Watanabe et al. 2008).
Session: Past, Present, and Future Collaborative Observational/Theory Programs
Authors: Keiji Yoshimura
Title: X-ray bright points around small emerging flux regions
Abstract: Small soft X-ray (SXR) brightenings are sometimes observed around emerging flux regions (EFRs). We study the development of SXR brightenings around EFRs with HINODE XRT data. Here we mainly use SoHO/MDI magnetograms to identify EFRs, because its field of view is wider than that of SOT.
We could categorize the identified EFRs into three groups by the SXR structures around them:
(1) no apparent structures,
(2) loop brightening connecting between two opposite polarity in the EFR, and
(3) brightening around the edge of the EFR.
For the group (2), the onset of the SXR brightenings delayed one hour or longer after the appearances of the EFRs in magnetograph data. Magnetic cancellations in magnetograms were found around some, not all, of the group (3) EFRs. In some of the EFRs, "secondary" emergence of magnetic flux seems to trigger the SXR brightenings.
The other characteristics of each group will be also presented.
Session: Solar Magnetic Activity
Authors: P.R. Young
Title: Density measurements at the base of the solar wind
Abstract: The density in coronal holes, measured in the low atmosphere, is an important quantity for models of the solar wind. Measurements are possible through remote sensing using emission line ratios in the extreme ultraviolet, however the measurements are difficult due to the low line intensities in the coronal holes. The high spatial resolution and high sensitivity of the EIS instrument are ideal for measuring the coronal hole density and new results will be presented using several different line ratios.
Session: Source of the Solar Wind/CME
Authors: Junwei Zhao, Alexander G. Kosovichev, Takashi Sekii
Title: Subsurface Structures and Flows in Active Regions and Polar Areas Obtained from Hinode
Abstract: Doppler observations from SOHO/MDI have made the derivation of subsruface structures and flow fields below active regions possible. The unprecedented high spatial resolution observation of G-band and CaH by Hinode is providing another possibility to study active region subsurface structures and flow fields with better spatial resolution than MDI, and more importantly, with observations other than Dopplergrams, i.e., intensity observations. Acoustic signals derived from intensity observations may not interfere with magnetic field as signals derived from Doppler velocities do. Furthermore, MDI observations cannot provide obsverations of polar area good enough for a helioseismic analysis of this area, where Hinode's high spatial resolution will provide a possibility for us. We will explore the subsurface flows in the solar South Pole area using Hinode observations.
Session: Local Helioseismology with Hinode
Authors: : Zharkov S. and Zharkova V.
Title: The 'heartbeat' of the Sun, or the characteristic periodicities deduced from long-term observations of the sunspot and background magnetic fields
Abstract: We present statistical analysis by using PCA method of the characteristic periods of the solar activity as a whole and in latitude and longitude deduced from the long series of sunspot and active region (toroidal) magnetic field and their tilts versus the background (poloidal) magnetic field data in different phases and for different solar cycles. We extracted a few phase relations between toroidal and poloidal fields in their latitudinal distributions. We have confirmed an oscillatory nature of the solar activity in longitude and detected for the cycle 23 the active longitude of about 200 degrees. Possible implications of this periodicities to theoretical models is discussed.
Session: Solar Magnetic Activity
Authors: : V.Zharkova, A. Kuznetsov and Siverskyi T.
Title: On a diagnostics of particle anisotropy in solar flares from hard X-ray and microwave emission with a Fokker-Plank approach with return current
Abstract: We investigate the effects of various energy transport mechanisms at electron precipitation into a flaring atmosphere. The distribution functions of precipitating electrons are obtained by solving Fokker-Plank equation with pitch-angle diffusion including the energy losses in collisions, self-induced electric field and converging magnetic field. The parameters of plasma are calculated by using hydrodynamic simulation of plasma heating by the same electron beam. The emission and polarization in hard X-rays and microwaves produced by beam electrons with different parameters at different times are calculated. The anisotropy of energetic electrons and effective depths of formation are found to strongly affect the resulting photon spectra from a flaring atmosphere and the beam parameters deduced from microwave and X-ray observations. The simulation results are fit to the simultaneous observations by RHESSI payload and Nobeyama radioheliograph obtained for a few flares providing a suitable tool for plasma diagnostics.
Session: Flare Physics
