Fine Structures and Overlying Loops of Confined Solar Flares

TL;DR

This study investigates the fine structures and magnetic configurations of three homologous confined solar flares, revealing how magnetic reconnection and overlying loops contribute to their confinement.

Contribution

It provides detailed observations of magnetic reconnection processes and the role of overlying loops in confining solar flares, enhancing understanding of flare confinement mechanisms.

Findings

Reconnection occurs between emerging small loops and large pre-existing loops.

Overlying large-scale loops do not break during flares, preventing eruption.

Magnetic reconnection triggers confined flares without eruption.

Abstract

Using the H$\alpha$ observations from the New Vacuum Solar Telescope at Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches are connected by small loops appearing as arch-shaped H$\alpha$ fibrils. There exists a reconnection between the small loops, and thus the H$\alpha$ fibrils change their configuration. The reconnection also occurs between a set of emerging H$\alpha$ fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote positive faculae, forming a typical three-legged structure. During the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. These direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive.