On the minimum temperature of the quiet solar chromosphere

TL;DR

This study uses advanced 2D radiation-MHD simulations to estimate the minimum temperature of the quiet solar chromosphere, revealing potential for even cooler regions than previously thought, and suggests observational and modeling strategies for further investigation.

Contribution

The paper introduces a detailed 2D simulation including non-LTE radiative transfer and non-equilibrium chemistry to estimate the chromosphere's minimum temperature, highlighting the possibility of cooler pockets.

Findings

Cool gas pockets down to 1660 K identified in simulations

Simulation overestimates radiative heating, indicating potential for even lower temperatures

Proposes observational and modeling approaches to explore cooler chromospheric regions

Abstract

aims: We aim to provide an estimate of the minimum temperature of the quiet solar chromosphere. methods: We perform a 2D radiation-MHD simulation spanning the upper convection zone to the lower corona. The simulation includes non-LTE radiative transfer and {an equation-of-state that includes non-equilibrium ionization of hydrogen and non-equilibrium H_2 molecule formation}. We analyze the reliability of the various assumptions made in our model in order to assess the realism of the simulation. results: Our simulation contains pockets of cool gas with down to 1660 K from 1 Mm up to 3.2 Mm height. It overestimates the radiative heating, and contains non-physical heating below 1660 K. Therefore we conclude that cool pockets in the quiet solar chromosphere might have even lower temperatures than in the simulation, provided that there exist areas in the chromosphere without significant magnetic heating. We suggest off-limb molecular spectroscopy to look for such cool pockets and 3D simulations including a local dynamo and a magnetic carpet to investigate Joule heating in the quiet chromosphere.