Thermal Instability in Post-Flare Plasmas.
Abstract
Satellite x-ray observations indicate that most solar flares produce a hot, dense plasma high up in the sun's corona. It is believed that this gas originates from lower regions of the atmosphere, specifically the chromosphere, were it is heated by a flare and evaporated into the corona. Optical observations have shown that the post-flare plasma does not cool uniformly, rather, small cold condensations form at the top of magnetic field arches while the bulk of the plasma remains at high temperature. Loop Prominence Systems are an example of this phenomenon. Dynamical processes connected with the flare event have been proposed as a mechanism for these types of active prominences. This report investigates the cooling of post-flare plasmas, and attempts to explain the formation of loop prominences as due to a thermal instability. At certain temperatures the solar plasma is known to be unstable to thermal perturbations because the radiation losses of this gas increase with decreasing temperature. A one-dimensional model is developed for active loop prominences. Magnetic fields present in post-flare regions are strong enough to dominate the plasma; hence, only motion and heat fluxes parallel to the field need to be considered. The relevant size scales and time scales are such that single-fluid MHD equations are valid. The model includes the effects of gravity, the geometry of the field and conduction losses to the chromosphere. A computer code for the solution of our set of equations has been contructed. From the results it is concluded that the non-uniform cooling of the postflare corona can be understood as a direct consequence of the temperature and density dependence of the radiative losses from a high-temperature solar plasma.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1976
- Accession Number
- ADA035775
Entities
People
- Spiro K. Antiochos
Organizations
- Stanford University