This work is an attempt to model the formation of solar quiescent prominences. The basis for these calculations is the qualitative model of Kuperus and Tandberg-Hanssen, in which the cool prominence material condenses out of the surrounding hot coronal plasma by the mechanism of thermal instability in the vicinity of a magnetically neutral sheet. The coronal plasma is described by the magnetohydrodynamic approximation and the resulting partial differential equations are solved in two dimensions using the Lax-Wendroff finite difference technique. Three classes of initial conditions are discussed. All cases involve a plasma at coronal conditions of temperature and density, with no material motion. The first class involves an atmosphere in vertical hydrostatic equilibrium and a vertical magnetic field with a gradient in field strength in the horizontal direction antisymmetric about a neutral field line. The second class involves identical magnetic fields but a plasma initially in lateral equilibrium of total pressure (gas plus magnetic). Two cases are investigated here, one with acceleration due to gravity set to its value at the solar surface, the other with the acceleration reduced by a factor of 10. The final class of cases involve closed magnetic fields approximated by arcs of concentric circular field lines above the solar surface. Only the case of lateral equilibrium and reduced gravity show any tendency to condense into a cool structure. In all other cases, large material motions are generated and this appears to inhibit condensation. It is concluded that initial conditions favorable to prominence formation need to be in both vertical and horizontal equilibrium. It is suggested that this might be achieved by including a third component of the magnetic field; including a finite electrical conductivity, allowing magnetic reconnection across the neutral sheet; or in the closed field cases, increasing the magnetic field strength so that the horizontal field component can provide support for the density excess.
- Pub Date:
- Physics: Astronomy and Astrophysics