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arXiv 1902.07772astro-ph.EP
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现今火星近地表相对湿度水平的全球季节变化

Global seasonal variations of the near-surface relative humidity levels on present-day Mars

B. Pál, Á. Kereszturi, F. Forget, M. D. Smith

摘要:

我们调查全球近地表相对湿度和相关属性的季节变化,如温度和水蒸气体积混合比在火星上使用的计算模型和测量数据。我们专注于当地时间凌晨2点的快照,以消除日射差异相关的日常影响,并能够比较基于LMDZ GCM的建模数据与MGS TES的观测结果的计算。我们通过研究火星年中的四个特定日期来研究季节效应,这四个日期是北方的春分、夏至、秋分和冬至。我们确定了三个特定的区域,近地表的相对湿度水平系统高于其附近,无论季节。我们发现,这些地区与低热惯性特征相吻合,这些特征控制着行星的地面温度,并且很可能覆盖着粒度小于$\sim$ 40 $μ$ m的未固结细尘。通过比较两个不同高度(近地面,距地面$\sim$ 23 m)的相对湿度、温度和水蒸气体积混合比的数据,我们证明了热惯性在确定近地面湿度水平中起着重要的作用。我们还注意到,在夜间,水蒸气水平在距地表$\sim$ 4米处下降。这与温度和热惯性值一起表明,水蒸气可能在上述三个区域的近地面大气和地面上在夜间凝结。这种凝结可能以盐水、细粒的润湿或潮解的形式出现。这项研究具体说明了当今火星表面上拟议冷凝的感兴趣区域,未来可能会通过现场测量进行检查。

英文摘要:

We investigate the global seasonal variations of near-surface relative humidity and relevant attributes, like temperature and water vapor volume mixing ratio on Mars using calculations from modelled and measurement data. We focus on 2 am local time snapshots to eliminate daily effects related to differences in insolation, and to be able to compare calculations based on modelling data from the LMDZ GCM with the observations of MGS TES. We study the seasonal effects by examining four specific dates in the Martian year, the northern spring equinox, summer solstice, autumn equinox and winter solstice. We identify three specific zones, where the near-surface relative humidity levels are systematically higher than in their vicinity regardless of season. We find that these areas coincide with low thermal inertia features, which control surface temperatures on the planet, and are most likely covered with unconsolidated fine dust with grain sizes less than $\sim$ 40$μ$m. By comparing the data of relative humidity, temperature and water vapor volume mixing ratio at two different heights (near-surface, $\sim$ 23 m above the surface), we demonstrate that the thermal inertia could play an important role in determining near-surface humidity levels. We also notice that during the night the water vapor levels drop at $\sim$ 4 m above the surface. This, together with the temperature and thermal inertia values, shows that water vapor likely condenses in the near-surface atmosphere and on the ground during the night at the three aforementioned regions. This condensation may be in the form of brines, wettening of the fine grains or deliquescence. This study specifies areas of interest on the surface of present day Mars for the proposed condensation, which may be examined by in-situ measurements in the future.

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