Overview of open issues in the physics of large solar flares

TL;DR

This review discusses the complex phenomena of magnetic reconnection in large solar flares, highlighting topological features, new analytical models, and recent numerical simulation insights to address open issues in solar flare physics.

Contribution

It summarizes current understanding and introduces new analytical models of magnetic reconnection, emphasizing the role of topological triggers and plasma resistivity in large solar flares.

Findings

Topological trigger phenomena are crucial for realistic flare models.

New models incorporate current layer rupture and plasma resistivity effects.

Recent simulations provide insights but raise new questions in flare physics.

Abstract

A broad variety of observational methods allows us to see the effect of magnetic reconnection in high-temperature strongly-magnetized plasma of the solar corona. Some specific features of the large-scale reconnection in large solar flares are summarized in this review but they are not investigated in detail yet. For example, an analysis of the topological peculiarities of magnetic field in active regions clearly shows that the so-called topological trigger phenomenon is necessary to allow for in order to construct realistic models for large solar flares and Coronal Mass Ejections (CMEs). However this is not a simple task. We discuss also some new analytical models of magnetic reconnection in a current layer with attached MHD discontinuities. These models take into account the possibility of a current layer rupture in the region of anomalous plasma resistivity. In the context of the numerical simulations on reconnection, a question on their interpretation is considered. Some new results obtained recently are briefly reviewed together with new questions of the solar flare physics to be studied.