The Role of fast magnetosonic waves in the release and conversion via reconnection of energy stored by a current sheet

TL;DR

This study uses a 2D zero-beta model to analyze how magnetic reconnection releases energy, with fast magnetosonic waves playing a key role in energy transfer and dissipation over extended periods.

Contribution

It reveals that most energy is converted into propagating fast magnetosonic waves, highlighting their significance in energy release and dissipation during magnetic reconnection.

Findings

Only 3%-11% of energy is dissipated near the current sheet.

25%-60% of energy remains as fast magnetosonic waves.

Waves reflect and bounce, causing prolonged energy dissipation.

Abstract

Using a simple two-dimensional, zero-beta model, we explore the manner by which reconnection at a current sheet releases and dissipates free magnetic energy. We find that only a small fraction (3%-11% depending on current sheet size) of the energy is stored close enough to the current sheet to be dissipated abruptly by the reconnection process. The remaining energy, stored in the larger-scale field, is converted to kinetic energy in a fast magnetosonic disturbance propagating away from the reconnection site, carrying the initial current and generating reconnection-associated flows (inflow and outflow). Some of this reflects from the lower boundary (the photosphere) and refracts back to the X-point reconnection site. Most of this inward wave energy is reflected back again, and continues to bounce between X-point and photosphere until it is gradually dissipated, over many transits. This phase of the energy dissipation process is thus global and lasts far longer than the initial purely local phase. In the process a significant fraction of the energy (25%-60%) remains as undissipated fast magnetosonic waves propagating away from the reconnection site, primarily upward. This flare-generated wave is initiated by unbalanced Lorentz forces in the reconnection-disrupted current sheet, rather than by dissipation-generated pressure, as some previous models have assumed. Depending on the orientation of the initial current sheet the wave front is either a rarefaction, with backward directed flow, or a compression, with forward directed flow.