Properties and Energetics of Magnetic Reconnection: I. Evolution of Flare Ribbons

TL;DR

This study investigates the evolution of flare ribbons and magnetic shear during solar flares, revealing correlations between shear reduction, X-ray emissions, and plasma heating, with implications for understanding energy release mechanisms.

Contribution

It introduces a detailed analysis of magnetic shear and flare ribbon evolution across multiple flares, linking morphological changes to energetic emissions and plasma heating.

Findings

Strong-to-weak shear evolution observed in flare cores

Hard X-ray emission increases as shear decreases

Plasma temperature rises during rapid ribbon spreading

Abstract

In this article, we measure the mean magnetic shear from the morphological evolution of flare ribbons, and examine the evolution of flare thermal and non-thermal X-ray emissions during the progress of flare reconnection. We analyze three eruptive flares and three confined flares ranging from GOES class C8.0 to M7.0. They exhibit well-defined two ribbons along the magnetic polarity inversion line (PIL), and have been observed by the Atmospheric Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager from the onset of the flare throughout the impulsive phase. The analysis confirms the strong-to-weak shear evolution in the core region of the flare, and the flare hard X-ray emission rises as the shear decreases. In eruptive flares in this sample, significant non-thermal hard X-ray emission lags the ultraviolet emission from flare ribbons, and rises rapidly when the shear is modest. In all flares, we observe that the plasma temperature rises in the early phase when the flare ribbons rapidly spread along the PIL and the shear is high. We compare these results with prior studies, and discuss their implications, as well as complications, related to physical mechanisms governing energy partition during flare reconnection.