OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines
OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines
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DOI：
10.5194/acp-20-5269-2020
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发表时间：
2019-12
影响因子：
6.3
通讯作者：
S. Noll;H. Winkler;O. Goussev;B. Proxauf
中科院分区：
文献类型：
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作者：
S. Noll;H. Winkler;O. Goussev;B. Proxauf
抽象的。OH气辉是地球中层顶区的一种重要的夜间发射。由于它是薄介质中的荧光辐射，电子基态的各种旋转振动OH能级上的布居分布不处于局部热力学平衡（LTE）。为了更好地理解这些非LTE效应，我们研究了数百条OH线，这些OH线是基于智利Cerro Paranal的高分辨率紫外和视觉中阶梯光谱仪的观测。我们导出的布居覆盖了v=3和9之间的振动能级，高达N=24的转动能级，以及解析时的单个Λ-双重态分量。由于这些结果的可靠性主要取决于所使用的爱因斯坦-A系数，我们测试了六个不同的集合，发现所有集合都存在明显的系统误差，特别是对于Q分支线和单个Λ-双重分量。为了最大限度地减少相同上水平的总体偏差，我们使用了布鲁克等人（2016）中最有希望的系数，并通过经验校正方法进一步改进了它们。由此产生的旋转水平的人口显示出一个明确的双峰为每个v，其特征在于由一个可能完全热化冷组件和热人口的旋转温度之间增加v=9和4之间从约700至约7000 K，和相应的贡献，在最低的N总人口减少了一个数量级。热人口的存在下，导致非LTE贡献的旋转温度在低N，这可以估计相当稳健的基础上的两个温度模型。的双峰性也清楚地表明，在OH发射层的有效发射高度的变化的人口的依赖。热化的程度随着层高度的增加而降低，这是由于热组分的比例较高。我们的高质量的人口数据是有希望的，以更好地了解OH热化过程。
Abstract. 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 Einstein-A coefficients used, we tested six different sets and found clear systematic errors in all of them, especially for Q-branch lines and individual Λ-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=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 two-temperature 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.