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DOI	10.5194/acp-20-5269-2020
	OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines
	Noll S.; Winkler H.; Goussev O.; Proxauf B.
发表日期	2020
ISSN	1680-7316
起始页码	5269
结束页码	5292
卷号	20 期号:9
英文摘要	OH airglow is an important nocturnal emission of the Earth's mesopause region. As it is chemiluminescent radiation in a thin medium, the population distribution over the various roto-vibrational OH energy levels of the electronic ground state is not in local thermodynamic equilibrium (LTE). In order to better understand these non-LTE effects, we studied hundreds of OH lines in a high-quality mean spectrum based on observations with the high-resolution Ultraviolet and Visual Echelle Spectrograph at Cerro Paranal in Chile. Our derived populations cover vibrational levels between v=3 and 9, rotational levels up to N=24, and individual λ-doublet components when resolved. As the reliability of these results critically depends on the EinsteinA coefficients used, we tested six different sets and found clear systematic errors in all of them, especially for Q-branch lines and individual 3-doublet components. In order to minimise the deviations in the populations for the same upper level, we used the most promising coefficients from Brooke et al. (2016) and further improved them with an empirical correction approach. The resulting rotational level populations show a clear bimodality for each v, which is characterised by a probably fully thermalised cold component and a hot population where the rotational temperature increases between v D 9 and 4 from about 700 to about 7000 K, and the corresponding contribution to the total population at the lowest N decreases by an order of magnitude. The presence of the hot populations causes non-LTE contributions to rotational temperatures at low N, which can be estimated quite robustly based on the twoerature model. The bimodality is also clearly indicated by the dependence of the populations on changes in the effective emission height of the OH emission layer. The degree of thermalisation decreases with increasing layer height due to a higher fraction of the hot component. Our high-quality population data are promising with respect to a better understanding of the OH thermalisation process. © 2020 Author(s).
语种	英语
scopus关键词	accuracy assessment; atmospheric chemistry; correction; electromagnetic radiation; hydroxide; image resolution; thermodynamics; Chile
来源期刊	ATMOSPHERIC CHEMISTRY AND PHYSICS
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/247804
作者单位	Institut für Physik, Universität Augsburg, Augsburg, Germany; Deutsches Fernerkundungsdatenzentrum, Deutsches Zentrum für Luft-und Raumfahrt, Weßling-Oberpfaffenhofen, Germany; Institut für Umweltphysik, Universität Bremen, Bremen, Germany; Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
推荐引用方式 GB/T 7714	Noll S.,Winkler H.,Goussev O.,et al. OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines[J],2020,20(9).
APA	Noll S.,Winkler H.,Goussev O.,&Proxauf B..(2020).OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines.ATMOSPHERIC CHEMISTRY AND PHYSICS,20(9).
MLA	Noll S.,et al."OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines".ATMOSPHERIC CHEMISTRY AND PHYSICS 20.9(2020).