MAGNETOHYDRODYNAMIC (MHD) SIMULATION OF SOLAR PROMINENCE FORMATION.

摘要

In this work, the formation of Kippenhahn-Schluter type solar prominences by chromospheric mass injection is studied via numerical simulation. The numerical model is based on a two-dimensional, time-dependent magnetohydrodynamic (MHD) theory. In addition, an analysis of gravitational thermal MHD instabilities related to condensation is performed by using the small perturbation method.;The conclusions are: (1) Both quiescent and active region prominences can be formed by chromospheric mass injection, provided certain optimum conditions are satisfied. The existence of these optimum conditions may explain why prominences do not appear on every neutral line. (2) Quiescent prominences cannot be formed without condensation, though enough mass is supplied from chromosphere. The mass of a quiescent prominence is composed of both the mass injected from the chromosphere and the mass condensed from the corona. On the other hand, condensation is not important to active region prominence formation. Active region prominences can be formed directly by injection of cool dense chromospheric mass. (3) In addition to channelling and supporting effects, the magnetic field plays another important role, i.e. containing the prominence material. A pit type magnetic field geometry has to be formed at the apex of the flux loop before the formation of the prominence. If the magnetic field is so strong that a pit cannot be formed at the apex before the cool dense material appears there, we will see the disappearance of prominence (in the quiescent prominence case) or the disappearance of the absorptive strands (in the active region prominence case). (4) In the model cases, prominences are supported by the Lorentz force, the gas pressure gradient and the mass injection momentum. The Lorentz force is the essential one. The support is of a dynamic nature. (5) Due to gravity, more MHD condensation instability modes appear in addition to the basic condensation mode. Among the additional modes, for example, is the Rayleigh - Taylor type mode. The growth rate of these modes is inversely proportional to the horizontal magnetic field strength.