THERMAL EQUILIBRIA IN SOLAR CORONAL MAGNETIC LOOPS - GRAVITATIONAL CONSIDERATIONS

Equations for thermal equilibria along coronal magnetic loops (with co nstant cross-sectional area) are solved in the absence and the presenc e of gravity. When the effect of gravity is negligible, loops may exis t with cool summits; these loops consist of two portions, an isotherma l portion at the summit and a non-isothermal portion near the footpoin t. In the presence of gravity, the two-component structure no longer e xists and there is a restriction (dependent on the heating) on the len gths of loops with cool summits. Loops with hot summits are cooled sli ghtly by the incorporation of gravity. A model of a cylindrical arcade is set up where the heating and the magnetic field vary with position . Hot arcades exist as do arcades with a vertical cool sheet surrounde d by hotter plasma - a situation that occurs for a prominence. It is a nticipated that loops with cool summits may exist for higher values of gravity when the loop area is allowed to vary with position.