Simulations of Small-Scale Explosive Events on the Sun

Small-scale explosive events or microflares occur throughout the chromospheric network of the Sun. They are seen as sudden bursts of highly Doppler shifted spectral lines of ions formed at temperatures in the range 2 x 10^4 - 5 x 10^5 K. They tend to occur near regions of canceling photospheric magnetic fields and are thought to be directly associated with magnetic field reconnection. Recent observations have revealed that they have a bi-directional jet structure reminiscent of Petschek reconnection. In this paper compressible MHD simulations of the evolution of a current sheet to a steady Petschek, jet-like configuration are computed using the Versatile Advection Code. We obtain velocity profiles that can be compared with recent ultraviolet line profile observations. By choosing initial conditions representative of magnetic loops in the solar corona and chromosphere, it is possible to explain the fact that at Sun center the jet flowing outward into the corona is more extended and seen before the jet flowing towards the chromosphere. Although this model can reproduce the high Doppler shifted components of the line profiles, the brightenings at low velocities, near the center of the bi-directional jet, cannot be explained by this simple MHD model.