Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes 

Silvina Guidoni Submitted: 20100707 10:02
We present a model for plasma heating produced by timedependent, spatially localized reconnection within a
flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity
which subsequently retract at Alfvénic speeds from the reconnection site. Heating occurs in gasdynamic shocks
(GDSs) which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of
reconnected flux tubes, including pressuredriven parallel dynamics as well as temperaturedependent, anisotropic
viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following
reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions.
Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong GDSs generated
by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the
tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a
steady state value, although this condition may not be reached in the short times involved in a flare. For realistic
solar coronal parameters, this steady state shock thickness might be as long as the entire flux tube. For strong
shocks at low Prandtl numbers, typical of the solar corona, the GDS consists of an isothermal subshock where all
the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the
heating occurs. We estimate the length of each of these subregions and the speed of their propagation.
Authors: Silvina Guidoni and Dana Longcope
Projects: None

Publication Status: ApJ (in press)
Last Modified: 20100707 12:07


