The solar chromosphere at high resolution with IBIS. IV. Dual-line evidence of heating in chromospheric network

TL;DR

This study uses high-resolution imaging spectroscopy of Halpha and Ca II lines to investigate the structure and heating processes of the solar chromosphere, revealing evidence of heating especially in network regions.

Contribution

It provides the first detailed comparison of Halpha and Ca II 854.2 nm profiles in the quiet Sun, highlighting their differences and common evidence of chromospheric heating.

Findings

Both lines show evidence of heating in network regions.

Halpha core width increases indicate heating.

Ca II brightness correlates with heating.

Abstract

The structure and energy balance of the solar chromosphere remain poorly known. We have used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Halpha and Ca II 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar in their rendering of the chromosphere, but that, nevertheless, both show evidence of chromospheric heating, particularly in and around network: Halpha in its core width, Ca II 854.2 in its brightness. We discuss venues for improved modeling.