Convective collapse and overstable oscillations in solar flux tubes

Abstract

The collapse of solar flux tubes by a convective instability is investigated. At the initial epoch it is assumed that the flux tube is in hydrostatic equilibrium and that it has the same temperature as the ambient medium. The superadiabatic stratification in the tube drives a convective instability. If the initial equilibrium is perturbed by the introduction of a small downflow in the tube, convective collapse occurs leading to magnetic field intensification. The final state consists of overstable oscillations with periods typically around 1000 sec. It is found that the surface magnetic field is in the observed 1 to 2 kG range. There is an oscillating flow (unidirectional at any instant) with an amplitude 1 to 2 km/sec and an average value around 0.