Energy Conversion and Electron Acceleration and Transport in 3D Simulations of Solar Flares

TL;DR

This study uses 3D MHD simulations to analyze energy conversion and electron acceleration mechanisms in solar flares, revealing the combined roles of reconnection, shocks, and turbulence in producing energetic electrons consistent with observations.

Contribution

It introduces a comprehensive 3D model solving Parker's transport equation to evaluate multiple acceleration mechanisms and their combined effects in solar flare electron energization.

Findings

Electrons are accelerated to hundreds of keV and MeV energies.

Acceleration occurs mainly at the current sheet, termination shock, and supra-arcade downflows.

Multiple mechanisms work together to produce observed energetic electron populations.

Abstract

Recent observations and simulations indicate that solar flares undergo extremely complex three-dimensional (3D) evolution, making 3D particle transport models essential for understanding electron acceleration and interpreting flare emissions. In this study, we investigate this problem by solving Parker's transport equation with 3D MHD simulations of solar flares. By examining energy conversion in the 3D system, we evaluate the roles of different acceleration mechanisms, including reconnection current sheet (CS), termination shock (TS), and supra-arcade downflows (SADs). We find that large-amplitude turbulent fluctuations are generated and sustained in the 3D system. The model results demonstrate that a significant number of electrons are accelerated to hundreds of keV and even a few MeV, forming power-law energy spectra. These energetic particles are widely distributed, with concentrations at the TS and in the flare looptop region, consistent with results derived from recent hard X-ray (HXR) and microwave (MW) observations. By selectively turning particle acceleration on or off in specific regions, we find that the CS and SADs effectively accelerate electrons to several hundred keV, while the TS enables further acceleration to MeV. However, no single mechanism can independently account for the significant number of energetic electrons observed. Instead, the mechanisms work synergistically to produce a large population of accelerated electrons. Our model provides spatially and temporally resolved electron distributions in the whole flare region and at the flare footpoints, enabling synthetic HXR and MW emission modeling for comparison with observations. These results offer important insights into electron acceleration and transport in 3D solar flare regions.