CORONAL LOOPS - CURRENT-BASED HEATING PROCESSES

A set of new experimental observations on the structure of the solar corona (Golub et al.) is used as input to the formulation of a theoretical model of magnetic field-related coronal heating processes. Field-aligned currents are assumed to be induced along coronal loops in thin current sheaths given that the rate of current density diffusion is relatively low. The excitation of instabilities involving magnetic reconnection is proposed to occur and convert the energy associated with the current-related magnetic field directly into particle energy. The estimated heating rate in this phase exceeds the energetic requirements of the loop and the heating process is envisioned as proceeding via short bursts corresponding to an intermittent disruption of the current sheath configuration. Because of the relatively low transverse thermal conduction, only a small fraction of the loop volume is heated to a much higher temperature than the average value. This is consistent with the experimental observations of low filling factors of hot plasmas in coronal loops (published by Martens et al.) Thus the proposed model involves a repeated sequence of dynamic events taking into account the observed loop topology, the differential emission measure distribution in the 10(6)-10(7) K range, the energy balance requirements in the loop, and the probable duty cycles involved in the heating process.