Solar flare radio pulsations as a signature of dynamic magnetic reconnection

TL;DR

This paper links solar flare radio pulsations to dynamic magnetic reconnection involving plasmoid formation, supported by observations and 2D MHD simulations, providing insights into particle acceleration and magnetic island coalescence.

Contribution

It introduces a model connecting radio pulsations to magnetic reconnection with plasmoid formation, supported by observational data and simulations.

Findings

Radio pulsations are caused by quasi-periodic particle acceleration episodes.

Magnetic reconnection involves formation and coalescence of magnetic islands.

Simulations support the dynamic reconnection model with plasmoid growth.

Abstract

Decimetric radio observations of the impulsive solar flare on October 5, 1992, 09:25 UT show a long series of quasi-periodic pulsations deeply modulating a continuum in the 0.6-2 GHz range that is slowly drifting toward lower frequencies. We propose a model in which the pulsations of the radio flux are caused by quasi-periodic particle acceleration episodes that result from a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalescence of magnetic islands (known as ``secondary tearing'' or ``impulsive bursty'' regime of reconnection), while a continuously growing plasmoid is fed by newly coalescing islands. Such a model, involving a current sheet and a growing plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama & Shibata 1998). We present two-dimensional MHD simulations of dynamic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasmoid formation in flares.