Morphological evidence for nanoflares heating warm loops in the solar corona

TL;DR

This study provides morphological evidence for nanoflare heating in the solar corona by observing the evolution of braided coronal loop strands and associated high-temperature emissions, supporting magnetic reconnection as a heating mechanism.

Contribution

It introduces a novel super-resolution imaging approach to detect strand evolution in coronal loops, revealing magnetic reconnection evidence at unprecedented spatial resolution.

Findings

Braided strands evolve into parallel strands with exchanged parts.

Transient high-temperature emissions appear at braiding footpoints.

Magnetic reconnection occurs within apparent single coronal loops.

Abstract

Nanoflares are impulsive energy releases by magnetic reconnection in the braided coronal magnetic field, which is a potential mechanism for heating the corona. However, there are still sporadic observations of the interchange of braiding structure segments and footpoints inside coronal loops, which is predicted to be the morphological evolution of the reconnecting magnetic bundles in the nanoflare picture. This work aims to detect the evolutions of the pairs of braiding strands within the apparent single coronal loops observed in Atmospheric Imaging Assembly (AIA) images. The loop strands are detected on two kinds of upsampled AIA 193 \AA\ images, which are obtained by upscaling the Point Spread Function matched AIA images via Bicubic interpolation and are generated using a super-resolution convolutional neural network, respectively. The architecture of the network is designed to map the AIA images to unprecedentedly high spatial resolution coronal images taken by High-resolution Coronal Imager (Hi-C) during its brief flight. At times, pairs of separate strands that appear braided together later evolved into pairs of almost parallel strands with completely exchanged parts. These evolutions offer morphological evidence that magnetic reconnections between the braiding strands have taken place, which is further supported by the appearance of transient hot emissions containing significant high-temperature components (T > 5MK) at the footpoints of the braiding structures. The brief appearances of the two rearranging strands support that magnetic reconnections have occurred within what appears to be a single AIA loop.