Effects of Non‐LTE Radiative Loss and Partial Ionization on the Structure of the Transition Region

Abstract

In this paper we address the question of how non-LTE radiative losses with partial ionization of hydrogen and helium a †ects the energetics and structure of the solar transition region. To accomplish this we have constructed theoretical models of a thin rigid magnetic Ñux tube with a steady material Ñow, which is embedded vertically in the solar atmosphere. These models include the e †ects of material Ñow, conduction, non-LTE radiative transfer in H and He, and partial ionization. We Ðnd from this study that the e †ect of non-LTE radiative transfer with partial ionization is signiÐcant near the base of the transition region at temperatures less than 2.5 ] 104 K. This leads to a 1 order of magnitude increase in the di †erential emission measure in comparison with the optically thin approximation with complete ionization in the low (less than 2.5 ] 104 K) temperature regime. Above this region the non-LTE and opacity e †ects are small. In the upÑow case the conductive and convective energy processes dominate to such a large extent that non-LTE radiative process and partial ionization are not important. In this work we also conÐrm the previous work of other authors who provided the explanation for why downÑowing transition region material is much more visible than upÑowing material. We present the results in a manner that gives a good physical understanding as to why this occurs.