Modelling H3+ in planetary atmospheres: effects of vertical gradients on observed quantities
Modelling H3+ in planetary atmospheres: effects of vertical gradients on observed quantities
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DOI：
10.1098/rsta.2019.0067
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发表时间：
2019-09-23
期刊：
影响因子：
5
通讯作者：
Schmidt, C. A.
中科院分区：
文献类型：
--
作者：
Moore, L.;Melin, H.;Schmidt, C. A.
自从大约30年前在木星的极光中被发现以来，H-3（+）离子一直是巨大行星高层大气的宝贵探测器。然而，绝大多数对行星H-3（+）辐射的监测都是从观测中得出的，这些观测依赖于通过发射层的列积分路径得出的参数。在这里，我们调查的影响，密度和温度梯度沿着这样的路径上测量的H-3（+）的光谱和由此产生的解释。在非等温大气中，从这样的观测中得到的H-3（+）柱密度被发现代表一个下限，从真实的大气值减少了20%或更多。天王星电离层的全球模拟显示，测量的H-3（+）温度变化通常归因于众所周知的太阳天顶角效应，而不是真实的大气变化的迹象。最后，根据这些见解，推导出垂直温度结构的初步方法，在木星上使用模型再现的电子密度和H-3（+）的测量。行星大气条件的绝对多样性和不确定性使这项工作无法提供全面的定量校正因子;尽管如此，我们还是说明了一些简单的方法，可以增强H-3（+）观测在理解行星大气方面已经强大的效用。这篇文章是讨论会议议题“氢分子离子的进展：H-3（+），H-5（+）及以后”的一部分。
Since its detection in the aurorae of Jupiter approximately 30 years ago, the H-3(+) ion has served as an invaluable probe of giant planet upper atmospheres. However, the vast majority of monitoring of planetary H-3(+) radiation has followed from observations that rely on deriving parameters from column-integrated paths through the emitting layer. Here, we investigate the effects of density and temperature gradients along such paths on the measured H-3(+) spectrum and its resulting interpretation. In a non-isothermal atmosphere, H-3(+) column densities retrieved from such observations are found to represent a lower limit, reduced by 20% or more from the true atmospheric value. Global simulations of Uranus' ionosphere reveal that measured H-3(+) temperature variations are often attributable to well-understood solar zenith angle effects rather than indications of real atmospheric variability. Finally, based on these insights, a preliminary method of deriving vertical temperature structure is demonstrated at Jupiter using model reproductions of electron density and H-3(+) measurements. The sheer diversity and uncertainty of conditions in planetary atmospheres prohibits this work from providing blanket quantitative correction factors; nonetheless, we illustrate a few simple ways in which the already formidable utility of H-3(+) observations in understanding planetary atmospheres can be enhanced.This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H-3(+), H-5(+) and beyond'.