Chromospheric heating due to cancellation of quiet Sun internetwork fields

TL;DR

This study investigates how cancellations of small-scale internetwork magnetic fields in the quiet Sun contribute to chromospheric heating, using high-resolution observations to analyze their energetics and dynamics.

Contribution

It provides detailed analysis of internetwork magnetic cancellations and their role in chromospheric heating, highlighting the discrepancy between observed event frequency and required energy contribution.

Findings

Cancellations last ~3 minutes in photosphere and ~12 minutes in upper layers.

Cancellations produce observable heating signatures in the chromosphere.

The observed cancellation frequency is insufficient to account for all chromospheric heating.

Abstract

The heating of the solar chromosphere remains one of the most important questions in solar physics. Our current understanding is that small-scale internetwork (IN) magnetic fields play an important role as a heating agent. Indeed, cancellations of IN magnetic elements in the photosphere can produce transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by magnetic reconnection of IN field lines. Although single events are not expected to release large amounts of energy, their global contribution to the chromosphere may be significant due to their ubiquitous presence in quiet Sun regions. In this paper we study cancellations of IN elements and analyze their impact on the energetics and dynamics of the quiet Sun atmosphere. We use high resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1-m Solar Telescope (SST) to identify cancellations of IN magnetic flux patches and follow their evolution. We find that, on average, these events live for ~3 minutes in the photosphere and ~12 minutes in the chromosphere and/or transition region. Employing multi-line inversions of the Mg II h & k lines we show that cancellations produce clear signatures of heating in the upper atmospheric layers. However, at the resolution and sensitivity accessible to the SST, their number density still seems to be one order of magnitude too low to explain the global chromospheric heating.