MHD discontinuities in solar flares: continuous transitions and plasma heating

TL;DR

This paper investigates the boundary conditions and transition solutions of ideal MHD discontinuities in solar flares, revealing how plasma heating depends on magnetic field configuration and flow conditions, with implications for solar corona temperature distributions.

Contribution

It provides a comprehensive analysis of continuous transitions between MHD discontinuities and derives expressions for plasma energy jumps, enhancing understanding of plasma heating mechanisms in solar flares.

Findings

Transition solutions satisfy two types of discontinuities.

Plasma heating is most effective near reconnecting current layers.

Temperature distribution in solar corona can be explained by these MHD processes.

Abstract

The boundary conditions for the ideal MHD equations on a plane dis- continuity surface are investigated. It is shown that, for a given mass flux through a discontinuity, its type depends only on the relation between inclina- tion angles of a magnetic field. Moreover, the conservation laws on a surface of discontinuity allow changing a discontinuity type with gradual (continu- ous) changes in the conditions of plasma flow. Then there are the so-called transition solutions that satisfy simultaneously two types of discontinuities. We obtain all transition solutions on the basis of the complete system of boundary conditions for the MHD equations. We also found the expression describing a jump of internal energy of the plasma flowing through the dis- continuity. Firstly, this allows constructing a generalized scheme of possible continuous transitions between MHD discontinuities. Secondly, it enables the examination of the dependence of plasma heating by plasma density and configuration of the magnetic field near the discontinuity surface, i.e., by the type of the MHD discontinuity. It is shown that the best conditions for heating are carried out in the vicinity of a reconnecting current layer near the areas of reverse currents. The result can be helpful in explaining the temperature distributions inside the active regions in the solar corona during flares observed by modern space observatories in soft and hard X-rays.