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arXiv 2005.09473astro-ph.EPphysics.space-ph
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CO +第一负带发射:火星高层大气中CO的示踪剂

CO+ first-negative band emission: A tracer for CO in the Martian upper atmosphere

Susarla Raghuram, Anil Bhardwaj

摘要:

最近,搭载在火星大气和挥发物演变N(MAVEN)卫星上的成像紫外光谱仪(IUVS)观测到了火星高层大气中的CO $^+$第一负带临边发射。我们的目标是探索火星高层大气中的光化学过程,这驱动了这一波段的发射。建立了一个光化学模式,研究了火星高层大气CO $^+$第一负带发射(B $^2Σ^+ \rightarrow$ X $^2Σ^+$)的激发过程。CO $_2$和来自两种不同模型的CO的数密度分布,即,利用火星气候数据库(MCD)和火星全球电离层-热层(MGIT)资料,确定了该带辐射的临边强度。在MCD和MGIT模型中,CO密度分别增加4倍和8倍,模拟的CO $^+$第一负带临边强度分布与IUVS/MAVEN观测结果一致。在这种情况下,该带发射的强度显著地由太阳光子和光电子对CO的电离决定,并且CO $_2$的解离电离的作用可以忽略不计。由于CO是COPDMATHABMM(B $^2Σ^+$)的主要来源,我们建议利用观测到的CO $^+$第一负带发射强度反演150 km以上高度的火星高层大气CO密度。

英文摘要:

Recently, Imaging Ultraviolet Spectrograph (IUVS) on-board Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite observed CO$^+$ first-negative band limb emission in the Martian upper atmosphere. We aim to explore the photochemical processes in the Martian upper atmosphere, which drives this band emission. A photochemical model is developed to study the excitation processes of CO$^+$ first-negative band emission (B$^2Σ^+ \rightarrow$ X$^2Σ^+$) in the upper atmosphere of Mars. The number density profiles of CO$_2$ and CO from two different models, viz., Mars Climate Database (MCD) and Mars Global Ionosphere-Thermosphere (MGIT) are used to determining the limb intensity of this band emission. On increasing the CO density by a factor of 4 and 8 in MCD and MGIT models, respectively, the modelled CO$^+$ first-negative band limb intensity profile is found to be consistent with IUVS/MAVEN observation. In this case, the intensity of this band emission is significantly determined by the ionization of CO by solar photons and photoelectrons, and the role of dissociative ionization of CO$_2$ is negligible. Since CO is the major source of the CO$^+$(B$^2Σ^+$), we suggest that the observed CO$^+$ first-negative band emission intensity can be used to retrieve the CO density in the Martian upper atmosphere for the altitudes above 150 km.

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