Evolution of Spatial Complexity in Flare Ribbon Substructure and Its Relationship to Magnetic Reconnection Dynamics

TL;DR

This study introduces a new method to quantify flare ribbon substructure evolution, revealing that increased spatial complexity correlates with stronger magnetic reconnection and current sheet fragmentation, providing a diagnostic tool for solar flare dynamics.

Contribution

The paper presents a novel quantitative approach using box-counting and correlation dimension mapping to analyze flare ribbon substructure evolution.

Findings

Higher ribbon complexity correlates with stronger HXR emission.

Ribbon complexity shows moderate correlation with non-thermal velocities.

Spatial complexity serves as a proxy for current-sheet fragmentation.

Abstract

Recent three-dimensional flare models suggest that flare-ribbon substructure is linked to the fragmentation of the reconnecting current sheet in the corona. Flare-ribbon substructure can therefore potentially serve as a unique diagnostic tool for physical processes in the flare current sheet. In this paper, we describe a new method to quantify the evolution of ribbon substructure, which first extract the ribbon's leading bright front and the quantifies its morphology using the box-counting dimension and Correlation Dimension Mapping (CDM). We first test our method using synthetic observations. We then find that when the flare ribbon boundary has more multi-spatial-scale features (higher box-counting dimension), hard X-ray (HXR) emission and magnetic reconnection rates are the strongest. We also find that the flare-ribbon complexity characterized by CDM has moderate correlation with the IRIS Si IV 1402.77 {\AA} non-thermal velocity (in the negative-polarity ribbon) and reconnection flux rates (in ribbons of both magnetic polarities). We conclude that the build-up of the spatial complexity of the ribbons at multiple spatial scales can serve as an observational proxy for current-sheet fragmentation in the corona.