Publication:

(1) Relentless Heating and Mass Insertion Into the Corona
De Pontieu, McIntosh (2010), Submitted to Science

Abstract:

Figure 1: Typical dynamic and thermal evolution of “type-II” spicules as observed by Hinode and SDO. These spicules are the result of discretized coronal heating events triggered low in the atmosphere. The panels on the left show (from top to bottom) the temporal evolution of a succession of type-II spicules visible as a dark feature in the top panel (Hα-0.868Å), and associated bright features in He II 304Å intensity and the running time-difference time series for He II 304Å, Fe IX 171Å, and Fe XIV 211Å. The space-time plots (right column) constructed along the axis of the spicule (dotted vertical white lines) show strong brightenings in all images at the bottom of the spicule during its initial stages. These brightenings then move upward with the same apparent speed (of order 70 km/s, see dashed diagonal guideline).

Combining observations of the Hinode and Solar Dynamics Observatory (SDO) spacecraft we have identified, and started to explore, discrete coronal heating events - for the first time tracking plasma heating from the low chromosphere (~10,000 K) into the extended corona (>2,000,000 K). These episodic heating events appear to be rooted in activity of the smallest (visible) scales of solar magnetism as observed by Hinode spectro-polarimeter, and have been unambiguously shown to manifest as very fine (~100km in diameter), rapidly traveling (~100km/s), and short-lived (10-100s) “Type-II” spicules, so-called to distinguish them from their classical siblings (≤1Mm across, 20-40 km/s, several minutes in duration). Tracking these rapid events through images of the Sun’s chromosphere provided by Hinode has revealed a one-to-one relationship with material that is considerably hotter moving upwards at the same apparent speed into the corona (with SDO) across many temperatures, often exceeding 2 million Kelvin.

These observations, such as shown in Figure 1, have provided a challenge to existing models of coronal heating by demonstrating that the majority of coronal temperature mass is dynamically forced out of the chromosphere pre-heated. The observed process provides strong constraint on the relentless cycling of mass between the Sun’s surface and outer solar atmosphere. Such knowledge will in turn permit the modeling of ultraviolet and extreme-ultraviolet radiation formation in the solar atmosphere that impinges on the Earth’s outer atmosphere.

Observational investigations are planned to isolate the relationship between magnetic field emergence, strength, geometry, and post-emergence evolution as likely “trigger” mechanisms for the launch and heating of the spicule material. It is imperative that the highest quality simulations of the middle atmospheric region are developed in tandem to place the observations in a quantitative context.

Publication:

(2) A Complication to the “Coronal Seismology” Paradigm
Tian, McIntosh, and DePontieu (2010), The Spectroscopic Signature of Quasi-periodic Upflows in Active Region Time Series, submitted to ApJ.

Abstract:

Figure: Temporal evolution of the XRT intensity and line parameters of Fe XII 195.12Å in the boundary of the active region. The left and right columns show the original and de-trended parameters, respectively. The values of Doppler shift and R-B are inverted so that a large value indicates more blue-shifted emission or stronger blueward asymmetry.

Quasi-periodic propagating disturbances are frequently observed in coronal intensity image sequences. These disturbances have historically been interpreted as being the signature of slow-mode magneto-acoustic waves propagating into the corona from the lower atmosphere and have been a strong driving influence of “Coronal Seismology”. Coronal Seismology uses the observed properties of the observed magnetohydrodynamic waves as probe of the physical properties (temperature, density, magnetic field, etc) of the solar atmosphere. De Pontieu & McIntosh (2010), and Tian, McIntosh & De Pontieu (2010) provided detailed analysis of Hinode EUV Imaging Spectrometer (EIS) time series observations of an active region shows strongly correlated, quasi-periodic, oscillations in intensity, Doppler shift, and line width. The enhancements in these “moments” of the line profile are generally accompanied by a faint, quasi-periodically occurring, excess emission at ~100 km/s in blue wing of the several high signal-to-noise coronal emission lines. These quasi-periodic upflows have been identified with high velocity mass flows triggered in the lower solar atmosphere and can be directly identified in simultaneous image sequences obtained by the Hinode X-Ray Telescope (XRT) as well as broadband imagers on the Solar Dynamics Observatory and STEREO spacecraft. The results of these papers appear to push the growing debate of “waves vs flows” in favor of the latter, as such correspondences are hard to reconcile in the wave paradigm although it should be noted that the insertion of a mass “plug” from the lower atmosphere will undoubtedly trigger the propagation of a wave through the corona. Future work will investigate the prevalence of one flavor of disturbance over the other and the balance between the two.

Publication:

(3) Ubiquitous Outflow in Coronal Holes has Deep Roots
McIntosh, et al. (2010), The Ubiquitous High Velocity Upflows of Coronal Holes as Observed With SDO, submitted to ApJ.

Abstract:

Figure: Results of applying the McIntosh et al (2008) mass motion tracking algorithm to the SDO/AIA image sequences of He II 304Å (~0.1MK), Fe IX 171Å(~1MK), Fe XII 193Å (~1.2MK), and Fe XIV 211Å (~2MK) from top to bottom. The left column shows the reference image from the start of the image time-series, the central column shows the inferred angle of the apparent motion detected relative to the vertical (solar North). The right column shows the inferred apparent speed of the motions detected in the image sequence. In each panel the 30DN iso-intensity contour of Fe XIV 211Å (e.g., bottom left panel) is over-plotted to denote the boundary between the coronal hole and quiet Sun plasma.

McIntosh et al. (2010) build upon recent spectroscopic investigations of the roots of the solar wind exploring multi-wavelength observations of a large equatorial coronal hole (ECH) with the instruments on the Solar Dynamics Observatory (SDO) taken on August 23, 2010.

The ECH observed was the source of a persistent 650 km/s solar wind observed by ACE. A clear feature of this ECH, like its polar counterparts, is the ubiquitous appearance of persistent small high-speed ejecta visible at a range of temperatures from emission formed at ~100,000K (He II 304Å) to ~1MK (Fe IX 171Å) throughout the ECH with the Atmospheric Imaging Assembly (AIA) across temperature wherever the polarity of the local magnetic field is of the same sign as the coronal hole net polarization as observed the Helioseismic and Magnetic Imager (HMI).

In regions of stronger magnetic field throughout the ECH the same jets exhibit emission from a plasma of ~2MK at their base. In a follow-up to recent spectroscopic efforts, we investigate the properties of these jets, applying space-time analysis and a novel algorithm designed to track motions in coronal imaging datasets to recover phase and angular information about the jets. While preliminary, the results of the latter suggest that the apparent speed (~75km/s) of the ejecta is consistent across temperatures from the chromosphere to corona in the stronger magnetic field regions the propagation angles are consistent with those inferred from the Milne-Eddington inversion of HMI Stokes polarization measurements.

The rooting of these ejecta in cooler chromospheric material and the consistent magnitude of the velocities is consistent with the emerging picture of an explosive and relentless mass transport through the chromosphere and low transition region in the form of dynamic spicules.