NONEQUILIBRIUM OF MAGNETIC-FLUX TUBES EMERGING INTO THE SOLAR CORONA

A lack of equilibrium of twisted magnetic flux tubes emerging from the photosphere into the corona is considered. Assuming mass and flux con servation in the tube and an isothermal tube that is in thermal equili brium with the surrounding plasma, it is shown that a sufficently rapi d temperature increase through the transition zone may lead to the los s of magnetohydrostatic equilibrium of the emerging flux tube due to t he enhancement of the plasma pressure inside the tube. The non-equilib rium leads to a rapid expansion of the tube to reach a new equilibrium state. The rise and expansion of the tube before and after the non-eq uilibrium are accompanied by an increase in the twist of the magnetic field. This may lead to the field exceeding the threshold for the onse t of the kink instability and a subsequent explosive release of magnet ic energy.