Chromospheric backradiation in ultraviolet continua and Halpha

TL;DR

This paper challenges recent claims about ultraviolet backradiation's influence on solar chromospheric ionization, demonstrating that photospheric radiation dominates and analyzing Halpha formation with significant backradiation effects.

Contribution

It refutes recent assertions on UV backradiation's impact and clarifies the dominant role of photospheric radiation in ionization balances and Halpha formation.

Findings

Ultraviolet backradiation does not significantly affect ionization in the solar atmosphere.

Photospheric radiation remains the primary influence on ionization balances.

Halpha formation involves notable backradiation across the opacity gap.

Abstract

A recent paper states that ultraviolet backradiation from the solar transition region and upper chromosphere strongly affects the degree of ionization of minority stages at the top of the photosphere, i.e., in the temperature minimum of the one-dimensional static model atmospheres presented in that paper. We show that this claim is incompatible with bservations and we demonstrate that the pertinent ionization balances are instead dominated by outward photospheric radiation, as in older static models. We then analyze the formation of Halpha in the above model and show that it has significant backradiation across the opacity gap by which Halpha differs from other strong scatttering lines.