SPRG Seminars
March 20, 2012:
"Plasma Heating and Asymmetric Magnetic Reconnection During Solar Eruptions"
Nick Murphy, Harvard-Smithsonian Center for Astrophysics
Several recent observational results suggest that plasma heating enters into the energy budget of coronal mass ejections (CMEs) at around the same order as the kinetic energy. The mechanisms responsible for the heating have not been identified, but candidates include small-scale relaxation, deposition of energy by non-thermal particles, and upflow from the flare/CME current sheet. First, I will present a time-dependent ionization analysis of a CME observed by the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. This analysis provides limits on the heating, and constrains which candidate mechanisms could be responsible for the heating. Next, I will consider heating by the CME current sheet in more detail. I will present resistive MHD simulations of X-line retreat during reconnection with asymmetric outflow. Most of the outflow energy is directed away from the obstructed exit so that more energy would be available for CME heating. Surprisingly, there is strong plasma flow at the X-line in the direction opposite X-line motion. By deriving an exact expression for the rate of X-line retreat, I show that this occurs because of diffusion of the normal component of the magnetic field. Last, I will present simulations of line-tied asymmetric reconnection in the context of flare and CME current sheets and show that the post-flare loops develop a characteristic skewed candle flame shape when the upstream magnetic fields are of unequal strength.