The formation of solar quiescent prominences by condensation

Abstract

We model the formation of solar quiescent prominences by solving numerically the non-linear, time-dependent, magnetohydrodynamic equations governing the condensation of the corona. A two-dimensional geometry is used. Gravitational and magnetic fields are included, but thermal conduction is neglected. The coronal fluid is assumed to cool by radiation and to be heated by the dissipation of mechanical energy carried by shock waves. A small, isobaric perturbation of the initial thermal and mechanical equilibrium is introduced and the fluid is allowed to relax. Because the corona with the given energy sources is thermally unstable, cooling and condensation result. When magnetic and gravitational fields are absent, condensation occurs isotropically with a strongly time-dependent growth rate, and achieves a density 18 times the initial density in 3.5 × 104 s. The rapidity of condensation is limited by hydrodynamical considerations, in contrast to the treatment of Raju (1968). When both magnetic and gravitational fields are included, the rate of condensation is inhibited and denser material falls. We conclude that: (1) condensation of coronal material due to thermal instability is possible if thermal conduction is inhibited; (2) hydrodynamical processes determine, in large part, the rate of condensation; (3) condensation can occur on a time scale compatible with the observed times of formation of quiescent prominences.