On the Short Dissipation Scales and Current-Sheet Properties of Low-Coronal EUV Brightenings

TL;DR

This study investigates small-scale brightenings in the low corona observed by Solar Orbiter, revealing two dissipation regimes and emphasizing the importance of current-sheet dissipation in quiet-Sun coronal heating.

Contribution

It identifies two distinct dissipation regimes and links small-scale brightenings to multi-scale energy release processes in the low corona.

Findings

Brightenings occur at 1-5 Mm heights with energies below nanoflares.

Impulsive brightenings last 1-10 seconds, consistent with fast magnetic reconnection.

Longer heating episodes last 10-100 seconds, indicating resistive dissipation.

Abstract

Solar Orbiter EUV observations reveal ubiquitous small-scale brightenings in the quiet-Sun low corona. We analyze the spatial and temporal dissipation scales of these events with a focus on the formation, evolution, and dissipation of associated current sheets. The brightenings are observed at heights of 1-5 Mm and span energies of 10^20 - 10^24 erg, well below the classical nanoflare regime, with the lowest-energy brightenings preferentially originating in the lowest coronal layers. Two distinct dissipation regimes are identified: impulsive brightenings with timescales of 1-10 s, consistent with fast, Alfvenic magnetic reconnection in low-beta plasma, and longer-lived heating episodes lasting 10-100 s, indicative of slower, resistive current-sheet dissipation under higher-beta conditions. The observed dissipation scales suggest a transition from kinetic-scale reconnection to macroscopic current-sheet heating in the low corona. These results support a multi-scale energy-release framework and highlight the role of low-altitude, small-scale current-sheet dissipation in quiet-Sun coronal heating.