Katharine K. Reeves

RECONNECTION OUTFLOWS AND CURRENT SHEET OBSERVED WITH HINODE/XRT IN THE 2008 APRIL 9 'CARTWHEEL CME' FLARE

Supra-arcade downflows (SADs) have been observed with Yohkoh/SXT (soft X-rays (SXR)), TRACE (extreme ultraviolet (EUV)), SOHO/LASCO (white light), SOHO/SUMER (EUV spectra), and Hinode/XRT (SXR). Characteristics such as low emissivity and trajectories, which slow as they reach the top of the arcade, are consistent with post-reconnection magnetic flux tubes retracting from a reconnection site high in the corona until they reach a lower-energy magnetic configuration. Viewed from a perpendicular angle, SADs should appear as shrinking loops rather than downflowing voids. We present X-ray Telescope (XRT) observations of supra-arcade downflowing loops (SADLs) following a coronal mass ejection (CME) on 2008 April 9 and show that their speeds and decelerations are consistent with those determined for SADs. We also present evidence for a possible current sheet observed during this flare that extends between the flare arcade and the CME. Additionally, we show a correlation between reconnection outflows observed with XRT and outgoing flows observed with LASCO.

ATMOSPHERIC IMAGING ASSEMBLY OBSERVATIONS OF HOT FLARE PLASMA

We present observations of hot plasma from solar eruptions recorded by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. AIA is the first narrowband instrument capable of taking images of hot plasma in the 5-15 MK range. We find that there are hot structures above flare loops, and that they are typically more diffuse and nebulous than the well-defined flare loops. Because of the narrowband response, high sensitivity, and high spatial resolution of AIA, these supra-arcade structures are visible in exquisite detail, particularly in the 131 A and 94 A channels. In one event, a C4.9 flare observed on 2010 November 3, hot plasma is seen to outline an erupting plasmoid and possibly a current sheet. We compare hot plasma observed with AIA to structures observed with the X-Ray Telescope on the Hinode mission and find that the plasma imaged in AIA contains more fine detail. These new AIA observations show that supra-arcade flare structures and coronal mass ejections are highly structured not only in space and time, but also in temperature. This thermal structuring is expected, based on modeling efforts, but has now been imaged directly for the first time over a large range of temperatures.

CURRENT SHEET ENERGETICS, FLARE EMISSIONS, AND ENERGY PARTITION IN A SIMULATED SOLAR ERUPTION

We investigate coronal energy flow during a simulated coronal mass ejection (CME). We model the CME in the context of the global corona using a 2.5D numerical MHD code in spherical coordinates that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The simulation domain extends from 1 to 20 Rs . To our knowledge, this is the first attempt to apply detailed energy diagnostics in a flare/CME simulation when these important terms are considered in the context of the MHD equations. We find that the energy conservation properties of the code are quite good, conserving energy to within 4% for the entire simulation (more than 6 days of real time). We examine the energy release in the current sheet as the eruption takes place, and find, as expected, that the Poynting flux is the dominant carrier of energy into the current sheet. However, there is a significant flow of energy out of the sides of the current sheet into the upstream region due to thermal conduction along field lines and viscous drag. This energy outflow is spatially partitioned into three separate components, namely, the energy flux flowing out the sides of the current sheet, the energy flowing out the lower tip of the current sheet, and the energy flowing out the upper tip of the current sheet. The energy flow through the lower tip of the current sheet is the energy available for heating of the flare loops. We examine the simulated flare emissions and energetics due to the modeled CME and find reasonable agreement with flare loop morphologies and energy partitioning in observed solar eruptions. The simulation also provides an explanation for coronal dimming during eruptions and predicts that the structures surrounding the current sheet are visible in X-ray observations.

Modeling the Cooling of Postflare Loops

We present a model for the cooling of postflare loops. In our model, we form an arcade that consists of hundreds of loops with offset formation times to simulate a rising reconnection site. An initial temperature and density is assumed in each loop, and then the scaling laws of Cargill, Mariska, & Antiochos are used to determine the evolution of the temperature and density in the loop. Once these quantities are found, they are passed through the instrument response functions for TRACE and the Yohkoh Soft X-Ray Telescope (SXT) to obtain intensities, which are integrated over the arcade to give a simulated light curve. This light curve is then compared to observed light curves from the 2000 July 14 X6 flare. We find that this multiloop, multithermal approach to simulating the flare cooling fits the observed data much better than a single-loop model. There are some discrepancies between our simulations and the observed data in the decay phase of the flare, however, which may be due to residual late-phase heating. We also find that the temperatures calculated by using SXT filter ratios are generally lower than the initial loop temperatures needed in the simulation to give a good fit to the observed data.

Field Line Shrinkage in Flares Observed by the X-Ray Telescope on Hinode

The X-Ray Telescope on Hinode has observed individual loops of plasma moving downward in a manner that is consistent with field line shrinkage in the aftermath of reconnection at higher altitudes. An on-disk B3.8 flare observed on 2007 May 2 has loops that clearly change in shape from cusp-shaped to more rounded. In addition, bright loops are observed that decrease in altitude with a speed of approximately 5 km s−1, and fainter, higher loop structures shrink with a velocity of 48 km s−1. A C2.1 flare observed on 2006 December 17 also has loops that change shape. Many bright features are seen to be moving downward in this event, and we estimate their speed to be around 2-4 km s−1. We measure the shrinkage in both of these events, and find that it is 17%-27%, which is consistent with theoretical predictions.

TEMPORAL EVOLUTION OF CHROMOSPHERIC EVAPORATION: CASE STUDIES OF THE M1.1 FLARE ON 2014 SEPTEMBER 6 AND X1.6 FLARE ON 2014 SEPTEMBER 10

With observations from the Interface Region Imaging Spectrograph (IRIS), we track the complete evolution of

FORWARD: A Toolset for Multiwavelength Coronal Magnetometry

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MAGNETIC STRUCTURE AND DYNAMICS OF THE ERUPTING SOLAR POLAR CROWN PROMINENCE ON 2012 MARCH 12

11 MK evaporation flows in an M1.1 flare on 2014 September 6 and an X1.6 flare on 2014 September 10. These hot flows, as indicated by the blueshifted Fe~{\sc{xxi}}~1354.08\AA{}~line, evolve smoothly with a velocity decreasing exponentially from

What Determines the Intensity of Solar Flare/CME Events?

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Thermal structure of current sheets and supra-arcade downflows in the solar corona

200~km~s