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

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Abstract
In this paper we address the question of how non-LTE radiative losses with partial ionization of hydrogen and helium affects the energetics and structure of the solar transition region. To accomplish this we have constructed theoretical models of a thin rigid magnetic flux tube with a steady material flow, which is embedded vertically in the solar atmosphere. These models include the effects of material flow, conduction, non-LTE radiative transfer in H and He, and partial ionization. We find from this study that the effect of non-LTE radiative transfer with partial ionization is significant 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 differential 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 effects are small. In the upflow 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 confirm the previous work of other authors who provided the explanation for why downflowing transition region material is much more visible than upflowing material. We present the results in a manner that gives a good physical understanding as to why this occurs.