Slow shocks and conduction fronts from Petschek reconnection of skewed magnetic fields: two-fluid effects

TL;DR

This paper investigates the structure of slow shocks and conduction fronts in magnetic reconnection with skewed magnetic fields, emphasizing the importance of two-fluid effects over single-fluid models for accurate predictions.

Contribution

It introduces a two-fluid model to analyze reconnection-driven slow shocks in skewed magnetic fields, revealing differences from traditional single-fluid magnetohydrodynamic predictions.

Findings

Electrons are heated indirectly, with heat flux below free-streaming limit.

Ion viscous stress is near fluid-treatable limit.

Electron conduction front extends ahead of slow shock within outflow jet.

Abstract

In models of fast magnetic reconnection, flux transfer occurs within a small portion of a current sheet triggering stored magnetic energy to be thermalized by shocks. When the initial current sheet separates magnetic fields which are not perfectly anti-parallel, i.e. they are skewed, magnetic energy is first converted to bulk kinetic energy and then thermalized in slow magnetosonic shocks. We show that the latter resemble parallel shocks or hydrodynamic shocks for all skew angles except those very near the anti-parallel limit. As for parallel shocks, the structures of reconnection-driven slow shocks are best studied using two-fluid equations in which ions and electrons have independent temperature. Time-dependent solutions of these equations can be used to predict and understand the shocks from reconnection of skewed magnetic fields. The results differ from those found using a single-fluid model such as magnetohydrodynamics. In the two-fluid model electrons are heated indirectly and thus carry a heat flux always well below the free-streaming limit. The viscous stress of the ions is, however, typically near the fluid-treatable limit. We find that for a wide range of skew angles and small plasma beta an electron conduction front extends ahead of the slow shock but remains within the outflow jet. In such cases conduction will play a more limited role in driving chromospheric evaporation than has been predicted based on single-fluid, anti-parallel models.