Magnetic Flux Ropes with a Current Shell As Flaring Solar Structures

Abstract

The models of force-free magnetic flux ropes differ in their internal current structure: strong electric currents are concentrated on the rope axis in one case and in a thin peripheral shell in the other one. In this paper we perform a comparative analysis of three new models of the second type. All force-free magnetic flux ropes have one common physical property leading to flare energy release: as the top of the loop rope exits into the solar chromosphere and corona, the external pressure keeping the rope from lateral expansion drops steadily; at some critical decrease in this pressure the longitudinal magnetic field of the rope approaches zero on the current inversion surface. At the same time, the azimuthal current \(j_{\varphi}(r)\) and the force-free parameter \(\alpha(r)\), while approaching the discontinuity on this surface, begin to increase indefinitely near it. This leads to the excitation of plasma ion-sound instability, a sharp decrease in the plasma conductivity, rapid magnetic energy dissipation in the rope, and the generation of super-Dreicer electric fields. The set of such processes in combination with the Parker effect, i.e., torque equalization along the rope axis with the Alfv’en speed, describes well the main manifestations of a solar flare.