Evolution of current sheets following the onset of enhanced resistivity

The sudden enhancement of the effective electrical resistivity in the preflare current sheet arising from the onset of a plasma micro-instability is considered an important aspect of these sheets in the solar atmosphere. Numerical and analytical solutions to the isothermal MHD equations are presented describing the evolution of a current sheet subsequent to such an enhancement in the resistivity. The solutions show that, if the initial width of the current sheet is less than the acoustic-diffusion length obtained by dividing the resistivity by the sound speed, isomagnetic shocks are formed. The shocks propagate outward from the center of the current sheet and are transformed into fast-mode magneto-acoustic waves when they reach the edges of the current sheet.