May 21, 2010, 12:00 pm - 1:00 pm
May 21, 2010, 12:00 pm - 1:00 pm
Comparing Solar-Flare Ion and Electron Acceleration
Albert Y. Shih (Solar Physics Laboratory)
Solar flares can accelerate both ions and electrons to high energies, with comparable energy content in each population. Gamma-ray and X-ray observations of the lines and continua produced by energetic ions and electrons probe the connection between these two populations. A comprehensive look at RHESSI flares finds proportional acceleration of ions and electrons at high energies, indicating a common acceleration process, while there is evidence for a separate acceleration process for lower-energy electrons. However, RHESSI gamma-ray images have shown significant spatial separations between where ions and electrons interact with the atmosphere. A new balloon instrument to advance such observations, the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS), will use novel technologies to provide unparalleled gamma-ray imaging and polarimetry capabilities and will prove these technologies for a future space-borne mission.
Evidence for Enhanced Particle Acceleration During a Plasmoid-Looptop Collision Observed with RHESSI
Ryan O. Milligan (Solar Physics Laboratory and Catholic University of America)
The standard flare model states that the primary release of energy occurs when magnetic field lines converge and reconnect along a current sheet in the corona, thereby energizing both the CME and the flare. In some cases multiple reconnection sites can develop resulting in the formation of plasmoids, or 'magnetic islands', along the current sheet. As magnetic field strength and electron density both decrease with height the vast majority of plasmoids observed close to the Sun tend to rise, often in sync with the CME. In this talk I will present observations of the first downward-moving plasmoid observed with RHESSI which occurred during the acceleration phase of the associated CME observed with STEREO. As the plasmoid collided with the top of the underlying flare loop, enhanced emission was observed in HXRs and radio waves suggesting that a secondary phase of particle acceleration took place. Comparisons will be made with a similar event observed by Yohkoh and a recent numerical simulation of plasmoid formation and propagation due to the tearing mode instability during current sheet formation.
Energy Transfer by an Enthalpy Flux in the Solar Atmosphere
Stephen Bradshaw (Solar Physics Laboratory)
Observations made by the Extreme ultra-violet Imaging Spectrometer (EIS) aboard the Hinode spacecraft have revealed persistent and pervasive Doppler-shifts in solar coronal emission lines, showing that the plasma is in a perpetual state of motion. In particular, the emission from active region cores is strongly red-shifted, indicating the presence of down-flowing material at temperatures near one million degrees K. The significance of these flows in an impulsively heated corona is two-fold: firstly, they are responsible for a substantial amount of energy loss from the corona (dominating thermal conduction losses); secondly, the energy transferred from the corona sustains the transition region against its radiative losses. Thus, the physics of coronal EUV loops can be understood as the interplay between the importance of energy transfer by an enthalpy flux and the energy loss by radiation.