HAO 2012 Profiles In Science: Dr. Scott McIntosh
Contact:
303-497-1544
mscott@ucar.edu
Section Head: Solar Transients and Space Weather
Dr. Scott McIntosh is a Scientist III and Section Head in the High Altitude Observatory of the National Center for Atmospheric Research. He received his PhD in Astrophysics in 1998 from the University of Glasgow, Scotland. His first work with HAO began in 1997 as a graduate student. His primary focus of research is chromospheric dynamics and understanding the physical connectivity between the Sun's cool surface and its considerably hotter corona. The resulting mass transport to and from the corona produces the radiation in the solar atmosphere that is most variable over a solar cycle. In recent times Scott has expanded this effort to study longer periods to assess if (and why) the underlying energetics of the star are changing.
Professional Website(s): Scott McIntosh
FY 2012 Highlights
(1) De Pontieu, McIntosh. 2011: The origins of hot plasma in the solar corona. Science, 331, 55.
Figure 1 caption: Demonstrating the persistent downward trend in underlying solar surface magnetism over the past four decades and its effect on the radiative and particulate outputs of our star. From McIntosh et al. (2012) “Hemispheric Asymmetries of Solar Photospheric Magnetism: Radiative, Particulate and Heliospheric Impacts”. Comparing the relative amplitude of the small and global spatial scale measurements used in the figures above from the present day back to 1970. We show the 28-day averaged values of the SOHO/VIRGO TSI (red dots); SOHO/MDI MRoI (green dots); SOHO/EIT Supergranular Network Radius (yellow dots); the “inverted” SOHO Solid State Recorder Single-Event-Flag Count (dark blue dots) with the longer solar wind speed (orange dots), Helium abundance (purple dots) from the OMNI database, with the “inverted” Oulu CRF (turquoise dots). Vertical dashes indicate the variance in that measurement over the temporal averaging applied. All of the timeseries (with the exception of the solar wind speed) are scaled to have the same dynamic range between 2001 and 2008 so that their relative amplitude changes can be compared and put in contrast with the longer records. The term “inverted” refers to a timeseries that has been rotated around its horizontal axis such that a peak is now a trough.
FY 2012 Publications
(1) McIntosh, Scott W.; Leamon, Robert J.; Gurman, Joseph B.; Olive, Jean-Phillipe; Cirtain, Jonathan, W.; Hathaway, David. H.; Burkepile, Joan; Miesch, Mark; Markel, Robert S.; Sitongia, Leonard. 2012: Hemispheric Asymmetries of Solar Photospheric Magnetism: Radiative, Particulate and Heliospheric Impacts. In press Astrophysical Journal.
Abtract: Among many other measurable quantities the summer of 2009 saw a considerable low in the radiative output of the Sun that was temporally coincident with the largest cosmic ray flux ever measured at 1AU. Combining measurements and observations made by the Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO) spacecraft we begin to explore the complexities of the descending phase of solar cycle 23, through the 2009 minimum into the ascending phase of solar cycle 24. A hemispheric asymmetry in magnetic activity is clearly observed and its evolution monitored and the resulting (prolonged) magnetic imbalance must have had a considerable impact on the structure and energetics of the heliosphere. While we cannot uniquely tie the variance and scale of the surface magnetism to the dwindling radiative and particulate output of the star, or the increased cosmic ray flux through the 2009 minimum, the timing of the decline and rapid recovery in early 2010 would appear to inextricably link them. These observations would appear to lend support to a picture where the hemispheres of the Sun have a (slightly) different meridional circulation rates and, furthermore, that the hemispheres are vary out of phase with each other. Studying historical sunspot records with this picture in mind shows that the northern hemisphere has been leading since the middle of the last century and that the hemispheric "dominance" has changed twice in the past 130 years. The observations presented give clear cause for concern, especially with respect to our present understanding of the processes that produce the surface magnetism in the (hidden) solar interior---only time will tell if our concern is well founded or not with the apparent dwindling of the radiative and particulate output over the past 30 years.
(2) McIntosh, Scott W.; De Pontieu, Bart. 2012: Estimating the "Dark" Energy Content of the Solar Corona. In press Astrophysical Journal.
Abtract: The discovery of ubiquitous low-frequency (3–5mHz) Alfvenic waves in the solar chromosphere (with Hinode/SOT), and corona (with CoMP and the Solar Dynamics Observatory, SDO) has provided some insight into the non-thermal energy content of the outer solar atmosphere. However, many questions remain about the true magnitude of the energy flux carried by these waves. Here we explore the apparent discrepancy in the resolved coronal Alfvenic wave amplitude (~0.5km/s) measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those of the Hinode and the SDO near the limb (~20km/s). We use a blend of observational data and a simple forward model of Alfvenic wave propagation to resolve this discrepancy and determine the Alfvenic wave energy content of the corona. Our results indicate that enormous line-of-sight superposition within the coarse spatio-temporal sampling of CoMP hides the strong wave flux observed by Hinode and SDO and leads to the large non-thermal line broadening observed. While this scenario has been assumed in the past, our observations with CoMP of a strong correlation between the non-thermal line broadening with the low amplitude, low frequency Alfvenic waves observed in the corona provide the first direct evidence of a wave-related non-thermal line broadening. By reconciling the diverse measurements of Alfvenic waves we establish large coronal non-thermal linewidths as direct signatures of the hidden, or “dark”, energy content in the corona, and provide preliminary constraints on the energy content of the wave motions observed.
(3) Wang, Xin; McIntosh, Scott W.; Curdt, Werner; Tian, Hui; Peter, Hardi; Xia, Li-Dong. 2012: Temperature Dependence of UV Line Parameters in Network and Internetwork Regions of the Quiet Sun and Coronal Holes. In press Astronomy and Astrophysics.
Abstract: We study the temperature dependence of the average Doppler shift and the non-thermal line width in network and internetwork regions for both the quiet Sun (QS) and the coronal hole (CH), by using observations of the Solar Ultraviolet Measurements of Emitted Radiation instrument on board the Solar and Heliospheric Observatory spacecraft. We obtain the average Doppler shift and non-thermal line width in the network regions of QS, internetwork regions of QS, network regions of CH, and internetwork regions of CH by applying a single-Gaussian fit to the line profiles averaged in each of the four regions. The formation temperatures of the lines we use cover the range from 104 to 1.2×106 K. A three-component toy model, which includes a rapid, weak upflow generated in the lower atmosphere, a nearly static background, and a slow cooling downflow, is built to explain the temperature dependence of the line parameters in the network regions. An enhancement of the Doppler shift magnitude and the non-thermal line width in network regions compared to the internetwork regions is reported. We also report that most transition region lines are less red-shifted (by 0–8km/s) and broader (by 0–5km/s) in the coronal hole compared to the counterparts of the quiet Sun. In internetwork regions, the difference of the Doppler shifts between the coronal hole and the quiet Sun is slightly smaller, especially for the lines with formation temperatures lower than 2×105K. And the three-component toy model can reproduce the variation of the line parameters with the temperature very well. Our results suggest that the physical processes in network and internetwork regions are different, and that one needs to separate network and internetwork when discussing dynamics and physical properties of the solar atmosphere. The agreement between the results of the observation and our model suggests that the temperature dependence of Doppler shifts and line widths might be caused by the different relative contributions of the three components at different temperatures. The results may shed new light on our understanding of the complex chromosphere-corona mass cycle.
(4) Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon; De Pontieu, Bart; Innes, Davina E.; Peter, Hardi. 2012: Persistent Doppler shift oscillations observed with HINODE/EIS in the solar corona: spectroscopic signatures of Alfvenic waves and recurring upflows. In press Astrophysical Journal. http://adsabs.harvard.edu/abs/2012arXiv1209.5286T.
Abstract: Using data obtained by the EUV Imaging Spectrometer (EIS) onboard Hinode, we have per- formed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width and profile asymmetry), apparent blue shift and blueward asymmetry throughout almost the en- tire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with formation temperatures between one and two million degrees. The global wavelets of these oscillations usually peak sharply around a period in the range of 3–6 minutes. No obvious profile asymmetry is found and the variation of the line width is typically very small. The intensity variation is often less than 2%. These oscillations are more likely to be signatures of kink/Alfven waves rather than flows. In a few cases there seems to be a pi/2 phase shift between the intensity and Doppler shift oscillations, which may suggest the presence of slow mode standing waves according to wave theories. However, we demonstrate that such a phase shift could also be produced by loops moving into and out of a spatial pixel as a result of Alfvenic oscillations. In this scenario, the intensity oscillations associated with Alfvenic waves are caused by loop displacement rather than density change.
(5) de Wijn, Alfred G.; Bethge, Christian; Tomczyk, Steven; McIntosh, Scott. 2012: The chromosphere and prominence magnetometer. In press proceedings of SPIE Astronomical Telescopes + Instrumentation. Conference 8446 (1-5 July 2012). http://adsabs.harvard.edu/abs/2012arXiv1207.0969D.
Abstract: The Chromosphere and Prominence Magnetometer (ChroMag) is conceived with the goal of quantifying the intertwined dynamics and magnetism of the solar chromosphere and in prominences through imaging spectro-polarimetry of the full solar disk. The picture of chromospheric magnetism and dynamics is rapidly developing, and a pressing need exists for breakthrough observations of chromospheric vector magnetic field measurements at the true lower boundary of the heliospheric system. ChroMag will provide measurements that will enable scientists to study and better understand the energetics of the solar atmosphere, how prominences are formed, how energy is stored in the magnetic field structure of the atmosphere and how it is released during space weather events like flares and coronal mass ejections. An integral part of the ChroMag program is a commitment to develop and provide community access to the "inversion" tools necessary for the difficult interpretation of the measurements and derive the magneto-hydrodynamic parameters of the plasma. Measurements of an instrument like ChroMag provide critical physical context for the Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS) as well as ground-based observatories such as the future Advanced Technology Solar Telescope (ATST).
(6) McIntosh, Scott W. 2012: Recent Observations of Plasma and Alfvénic Wave Energy Injection at the Base of the Fast Solar Wind. Space Science Reviews (in press). http://adsabs.harvard.edu/doi/10.1007/s11214-012-9889-x.
Abstract: We take stock of recent observations that identify the episodic plasma heating and injection of Alfvénic energy at the base of fast solar wind (in coronal holes). The plasma heating is associated with the occurrence of chromospheric spicules that leave the lower solar atmosphere at speeds of order 100 km/s, the hotter coronal counterpart of the spicule emits radiation characteristic of root heating that rapidly reaches temperatures of the order of 1 MK. Furthermore, the same spicules and their coronal counterparts ("Propagating Coronal Disturbances"; PCD) exhibit large amplitude, high speed, Alfvénic (transverse) motion of sufficient energy content to accelerate the material to high speeds. We propose that these (disjointed) heating and accelerating components form a one-two punch to supply, and then accelerate, the fast solar wind. We consider some compositional constraints on this concept, extend the premise to the slow solar wind, and identify future avenues of exploration.
(7) Kiddie, G.; De Moortel, I.; Del Zanna, G.; McIntosh, S. W.; Whittaker, I. 2012: Propagating Disturbances in Coronal Loops: A Detailed Analysis of Propagation Speeds. Solar Physics, 279, 2, 427–452 (SoPh Homepage). DOI: 10.1007/s11207-012-0042-5. http://adsabs.harvard.edu/abs/2012SoPh..279..427K.
Abstract: Quasi-periodic disturbances have been observed in the outer solar atmosphere for many years. Although first interpreted as upflows (Schrijver et al., Solar Phys. 187, 261, 1999) they have been widely regarded as slow magneto-acoustic waves, due to their observed velocities and periods. However, recent observations have questioned this interpretation, as periodic disturbances in Doppler velocity, line width, and profile asymmetry were found to be in phase with the intensity oscillations (De Pontieu and McIntosh, 2010; Tian, McIntosh, and De Pontieu, 2011) suggesting that the disturbances could be quasi-periodic upflows. Here we conduct a detailed analysis of the velocities of these disturbances across several wavelengths using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We analyzed 41 examples, including both sunspot and non-sunspot regions of the Sun. We found that the velocities of propagating disturbances (PDs) located at sunspots are more likely to be temperature dependent, whereas the velocities of PDs at non-sunspot locations do not show a clear temperature dependence. This suggests an interpretation in terms of slow magneto-acoustic waves in sunspots but the nature of PDs in non-sunspot (plage) regions remains unclear. We also considered on what scale the underlying driver is affecting the properties of the PDs. Finally, we found that removing the contribution due to the cooler ions in the 193 Å wavelength suggests that a substantial part of the 193 Å emission of sunspot PDs can be attributed to the cool component of 193 Å.
(8) Tian, H.; McIntosh, S. W.; De Pontieu, B. 2012: Two Components of the Coronal Emission Revealed by Both Spectroscopic and Imaging Observations. The Fifth Hinode Science Meeting. ASP Conference Series, 456, Proceedings of a conference held 10–14 October 2011 at Royal Sonesta Hotel, Cambridge, Massachusetts. Edited by Leon Golub, Ineke De Moortel and Toshifumi Shimizu. San Francisco: Astronomical Society of the Pacific, p.97. http://adsabs.harvard.edu/abs/2012ASPC..456...97T.
Abstract: X-ray and EUV imaging observations often reveal quasi-periodic propagating disturbances along the fan-like structures at edges of active regions. These disturbances have historically been interpreted as being signatures of slow-mode magnetoacoustic waves propagating into the corona. Recent spectroscopic observations have revealed the ubiquitous presence of blueward asymmetries of EUV emission line profiles. Such asymmetries suggest that there are at least two emission components: a primary component accounting for the background emission and a secondary component associated with high-speed upflows. Thus, a single Gaussian fit can not reflect the real physics here. Through joint imaging and spectroscopic observations, we find a clear association of the secondary component with the upward propagating disturbances and conclude that they are more likely to be real plasma outflows (small-scale recurring jets) rather than slow waves. These outflows may result from impulsive heating processes in the lower transition region or chromosphere and could be an efficient means to provide hot plasma into the corona and possibly also solar wind.
(9) Sechler, M.; McIntosh, S. W.; Tian, H.; De Pontieu, B. 2012: Hinode/EIS Line Profile Asymmetries and Their Relationship with the Distribution of SDO/AIA Propagating Coronal Disturbance Velocities. 4th Hinode Science Meeting: Unsolved Problems and Recent Insights, ASP Conference series, 455, proceedings of a conference held 11-15 October 2010 in Palermo, Italy. Edited by Luis R. Bellot Rubio, Fabio Reale, and Mats Carlsson. San Francisco: Astronomical Society of the Pacific, 2012, p.361. http://adsabs.harvard.edu/abs/2012ASPC..455..361S.
Abstract: Using joint observations from Hinode/EIS and the Atmospheric Imaging Array (AIA) on the Solar Dynamics Observatory (SDO) we explore the asymmetry of coronal EUV line profiles. We find that asymmetries exist in all of the spectral lines studied, and not just the hottest lines as has been recently reported in the literature. Those asymmetries indicate that the velocities of the second emission component are relatively consistent across temperature and consistent with the apparent speed at which material is being inserted from the lower atmosphere that is visible in the SDO/AIA images as propagating coronal disturbances. Further, the observed asymmetries are of similar magnitude (a few percent) and width (determined from the RB analysis) across the temperature space sampled and in the small region studied. Clearly, there are two components of emission in the locations where the asymmetries are identified in the RB analysis, their characteristics are consistent with those determined from the SDO/AIA data. There is no evidence from our analysis that this second component is broader than the main component of the line.
(10) McIntosh, Scott W.; Tian, Hui; Sechler, Marybeth; De Pontieu, Bart. 2012: On the Doppler Velocity of Emission Line Profiles Formed in the "Coronal Contraflow" that Is the Chromosphere-Corona Mass Cycle. The Astrophysical Journal, 749, 1, article id. 60. DOI: 10.1088/0004-637X/749/1/60. http://adsabs.harvard.edu/abs/2012ApJ...749...60M.
Abstract: This analysis begins to explore the complex chromosphere-corona mass cycle using a blend of imaging and spectroscopic diagnostics. Single Gaussian fits (SGFs) to hot emission line profiles (formed above 1 MK) at the base of coronal loop structures indicate material blueshifts of 5–10 km/s, while cool emission line profiles (formed below 1 MK) yield redshifts of a similar magnitude—indicating, to zeroth order, that a temperature-dependent bifurcating flow exists on coronal structures. Image sequences of the same region reveal weakly emitting upward propagating disturbances in both hot and cool emission with apparent speeds of 50–150 km/s. Spectroscopic observations indicate that these propagating disturbances produce a weak emission component in the blue wing at commensurate speed, but that they contribute only a few percent to the (ensemble) emission line profile in a single spatio-temporal resolution element. Subsequent analysis of imaging data shows material "draining" slowly (~10 km/s) out of the corona, but only in the cooler passbands. We interpret the draining as the return flow of coronal material at the end of the complex chromosphere-corona mass cycle. Further, we suggest that the efficient radiative cooling of the draining material produces a significant contribution to the red wing of cool emission lines that is ultimately responsible for their systematic redshift as derived from an SGF when compared to those formed in hotter (conductively dominated) domains. The presence of counterstreaming flows complicates the line profiles, their interpretation, and asymmetry diagnoses, but allows a different physical picture of the lower corona to develop.
(11) Tian, Hui; McIntosh, Scott W.; Xia, Lidong; He, Jiansen; Wang, Xin. 2012: What can We Learn about Solar Coronal Mass Ejections, Coronal Dimmings, and Extreme-ultraviolet Jets through Spectroscopic Observations? The Astrophysical Journal, 748, 2,106. DOI: 10.1088/0004-637X/748/2/106. http://adsabs.harvard.edu/abs/2012ApJ...748..106T.
Abstract: Solar eruptions, particularly coronal mass ejections (CMEs) and extreme-ultraviolet (EUV) jets, have rarely been investigated with spectroscopic observations. We analyze several data sets obtained by the EUV Imaging Spectrometer on board Hinode and find various types of flows during CMEs and jet eruptions. CME-induced dimming regions are found to be characterized by significant blueshift and enhanced line width by using a single Gaussian fit, while a red-blue (RB) asymmetry analysis and an RB-guided double Gaussian fit of the coronal line profiles indicate that these are likely caused by the superposition of a strong background emission component and a relatively weak (~10%), high-speed (~100 km/s) upflow component. This finding suggests that the outflow velocity in the dimming region is probably of the order of 100 km/s, not ~20 km/s as reported previously. These weak, high-speed outflows may provide a significant amount of mass to refill the corona after the eruption of CMEs, and part of them may experience further acceleration and eventually become solar wind streams that can serve as an additional momentum source of the associated CMEs. Density and temperature diagnostics of the dimming region suggest that dimming is primarily an effect of density decrease rather than temperature change. The mass losses in dimming regions as estimated from different methods are roughly consistent with each other, and they are 20%–60% of the masses of the associated CMEs. With the guide of RB asymmetry analysis, we also find several temperature-dependent outflows (speed increases with temperature) immediately outside the (deepest) dimming region. These outflows may be evaporation flows that are caused by the enhanced thermal conduction or nonthermal electron beams along reconnecting field lines, or induced by the interaction between the opened field lines in the dimming region and the closed loops in the surrounding plage region. In an erupted CME loop and an EUV jet, profiles of emission lines formed at coronal and transition region temperatures are found to exhibit two well-separated components, an almost stationary component accounting for the background emission and a highly blueshifted (~200 km/s) component representing emission from the erupting material. The two components can easily be decomposed through a double Gaussian fit, and we can diagnose the electron density, temperature, and mass of the ejecta. Combining the speed of the blueshifted component and the projected speed of the erupting material derived from simultaneous imaging observations, we can calculate the real speed of the ejecta.
(12) Judge, Philip G.; de Pontieu, Bart; McIntosh, Scott W.; Olluri, Kosovare. 2012: The Connection of Type II Spicules to the Corona. The Astrophysical Journal, 746, 2, 158. DOI: 10.1088/0004-637X/746/2/158. http://adsabs.harvard.edu/abs/2012ApJ...746..158J.
Abstract: We examine the hypothesis that plasma associated with "Type II" spicules is heated to coronal temperatures, and that the upward moving hot plasma constitutes a significant mass supply to the solar corona. One-dimensional hydrodynamical models including time-dependent ionization are brought to bear on the problem. These calculations indicate that heating of field-aligned spicule flows should produce significant differential Doppler shifts between emission lines formed in the chromosphere, transition region, and corona. At present, observational evidence for the computed 60-90 km s-1 differential shifts is weak, but the data are limited by difficulties in comparing the proper motion of Type II spicules with spectral and kinematic properties of an associated transition region and coronal emission lines. Future observations with the upcoming infrared interferometer spectrometer instrument should clarify if Doppler shifts are consistent with the dynamics modeled here.
(13) McIntosh, Scott W.; Kiefer, Kandace K.; Leamon, Robert J.; Kasper, Justin C.; Stevens, Michael L. 2011: Solar Cycle Variations in the Elemental Abundance of Helium and Fractionation of Iron in the Fast Solar Wind: Indicators of an Evolving Energetic Release of Mass from the Lower Solar Atmosphere. The Astrophysical Journal Letters, 740, 1, L23. DOI: 10.1088/2041-8205/740/1/L23. http://adsabs.harvard.edu/abs/2011ApJ...740L..23M.
Abstract: We present and discuss the strong correspondence between evolution of the emission length scale in the lower transition region and in situ measurements of the fast solar wind composition during the most recent solar minimum. We combine recent analyses demonstrating the variance in the (supergranular) network emission length scale measured by the Solar and Heliospheric Observatory (and STEREO) with that of the helium abundance (from Wind) and the degree of iron fractionation in the solar wind (from the Advanced Composition Explorer and Ulysses). The net picture developing is one where a decrease in the helium abundance and the degree of iron fractionation (approaching values expected of the photosphere) in the fast wind indicate a significant change in the process loading material into the fast solar wind during the recent solar minimum. This result is compounded by a study of the helium abundance during the space age using the NASA OMNI database, which shows a slowly decaying amount of helium being driven into the heliosphere over the course of several solar cycles.