# Magnetic filed dynamics and varying plasma emission in large coronal loops

## TL;DR

This paper investigates magnetic activity and plasma emission in large coronal loops, revealing how magnetic reconnection at footpoints influences loop brightening and plasma heating, with detailed observations from SDO and GST.

## Contribution

It provides new insights into the magnetic reconnection processes at coronal loop footpoints and their role in plasma heating and emission in the solar atmosphere.

## Key findings

- Loop brightening linked to magnetic flux emergence and cancellation.
- Reconnection occurs in the lower chromosphere at plage edges.
- Plasma filling and cooling propagate along loops at 90-110 km/s.

## Abstract

In this study we report detailed observations of magnetic environment at four footpoints of two warm coronal loops observed on 5 May 2016 in NOAA AR 12542 (Loop I) and 17 Dec 2015 in NOAA AR 12470 (Loop II). These loops were connecting a plage region with sunspot periphery (Loop I) and a sunspot umbra (Loop II). We used Solar Dynamics Observatory (SDO) and Goode Solar Telescope (GST) data to describe the phenomenon and understand its causes. The study indicates loop brightening episodes were associated with magnetic flux emergence and cancellation processes observed in SDO's Helioseismic and Magnetic Imager (HMI) and GST's Near InfraRed Imaging Spectrapolarimeter (NIRIS) data. The observed activity was driven by magnetic reconnection between small-scale emerging dipoles and large-scale pre-existing fields, suggesting that the reconnection occurred in the lower chromosphere at the edge of an extended plage region, where the loops were rooted. We suggest that plasma, evaporated during these reconnection events, gradually filled the loops and as it cooled the visible density front propagated from one footpoint of the loop to another at a rate of 90-110 km s$^{-1}$. This study also indicates that at least some of the bright loops seen in SDO Atmospheric Imaging Assembly images rooted in sunspot umbra may be heated due to magnetic activity taking place at the remote (non-sunspot) footpoint.