Solar Spectroscopy and (Pseudo-)Diagnostics of the Solar Chromosphere

TL;DR

This paper reviews current solar spectrometry techniques, compares various diagnostics of the solar chromosphere, and discusses their effectiveness in revealing chromospheric heating and the connection to coronal heating and solar wind.

Contribution

It provides a critical comparison of spectroscopic diagnostics, highlighting limitations and clarifying which diagnostics truly reflect chromospheric conditions.

Findings

Balmer Halpha reveals the closed-field chromosphere

Many diagnostics do not accurately represent chromospheric heating

Open-field chromosphere diagnostics are limited in optical wavelengths

Abstract

I first review trends in current solar spectrometry and then concentrate on comparing various spectroscopic diagnostics of the solar chromosphere. Some are actually not at all chromospheric but just photospheric or clapotispheric and do not convey information on chromospheric heating, even though this is often assumed. Balmer Halpha is the principal displayer of the closed-field chromosphere, but it is unclear how chromospheric fibrils gain their large Halpha opacity. The open-field chromosphere seems to harbor most if not all coronal heating and solar wind driving, but is hardly seen in optical diagnostics.