Spontaneous current-layer fragmentation and cascading reconnection in solar flares: II. Relation to observations

TL;DR

This study links high-resolution MHD simulations of solar flare current sheet fragmentation and cascading reconnection to observable features in flare ribbons, providing a model for energy transfer and emission structures.

Contribution

It extends previous simulations by deriving observable signatures of flux-rope cascades in flare ribbons, connecting theoretical models with actual solar observations.

Findings

Hierarchical distribution of non-ideal regions in the current sheet.

Predicted emission structures match observed flare ribbon kernels.

Cascading reconnection facilitates energy transfer across scales.

Abstract

In the paper by B\'arta et al. (arXive:astro-ph:/1011.4035, 2010) the authors addressed some open questions of the CSHKP scenario of solar flares by means of high-resolution MHD simulations. They focused, in particular, on the problem of energy transfer from large to small scales in decaying flare current sheet (CS). Their calculations suggest, that magnetic flux-ropes (plasmoids) are formed in full range of scales by a cascade of tearing and coalescence processes. Consequently, the initially thick current layer becomes highly fragmented. Thus, the tearing and coalescence cascade can cause an effective energy transfer across the scales. In the current paper we investigate whether this mechanism actually applies in solar flares. We extend the MHD simulation by deriving model-specific features that can be looked for in observations. The results of the underlying MHD model showed that the plasmoid cascade creates a specific hierarchical distribution of non-ideal/acceleration regions embedded in the CS. We therefore focus on the features associated with the fluxes of energetic particles, in particular on the structure and dynamics of emission regions in flare ribbons. We assume that the structure and dynamics of diffusion regions embedded in the CS imprint themselves into structure and dynamics of flare-ribbon kernels by means of magnetic-field mapping. Using the results of the underlying MHD simulation we derive the expected structure of ribbon emission and we extract selected statistical properties of the modelled bright kernels. Comparing the predicted emission and its properties with the observed ones we obtain a good agreement of the two.