Abstract
Lower atmosphere variations in the martian water vapour and hydrogen abundance during the late southern summer regional-scale dust storm from LS = 326.1°–333.5° Mars Year34 (18th-31st January 2019) and their associated effect on hydrogen escape are investigated using a multi-spacecraft assimilation of atmospheric retrievals into a Martian global circulation model. The dusty conditions led to an elevation of the hygropause and associated increase in middle atmosphere hydrogen at the peak of the dust storm, which was particularly intense in Mars Year34. This response has an important effect on water loss during this time period, quantification of which can provide a more robust calculation of the integrated loss of water through time on Mars and better insight to planetary evolution. The influx of water vapour to higher altitudes led to an associated increase in hydrogen through photolysis of water vapour and a hydrogen escape rate of around 1.0×109 cm−2s−1, meaning the late southern summer regional-scale dust storm in Mars Year34 enhanced water loss rates on Mars to levels observed during global-scale dust storms. The water loss rate during the late southern summer regional-scale dust storm, also known as a C storm, led to around 15% of the total annual water loss during only 5% of the year and was at least three times stronger than the much less dusty C storm event in Mars Year30. These results demonstrate that interannual variations in the strength of the late southern summer regional-scale dust storm must be considered when calculating the integrated loss of water on Mars, an important quantity to constrain in relation to the potential habitability of Mars.
Highlights
The past climate of Mars is generally considered to have been much wetter than the present (Carr and Head, 2010; Ehlmann and Edwards, 2014, and references therein)
A multi-spacecraft assimilation of ExoMars Trace Gas Orbiter (TGO) and Mars Reconnaissance Orbiter retrievals into the Open University (OU) modelling group global circulation model (GCM) has been performed to investigate the lower atmosphere distribution of water vapour and hydrogen during the Mars Year (MY) 34 C storm
These 4-D simulations have been coupled to an upper atmosphere 1-D photochemical model to calculate global hydrogen escape rates associated with the MY 34 C storm, a intense regional dust event
Summary
The past climate of Mars is generally considered to have been much wetter than the present (Carr and Head, 2010; Ehlmann and Edwards, 2014, and references therein). During the time period of the MY 34 C storm unobserved by ExoMars TGO, we can still constrain model simulations of the water/hydrogen activity using observations of the temperature and dust distribution from the Mars Climate Sounder (MCS) aboard the Mars Reconnaissance Orbiter (MRO) spacecraft (Kleinböhl et al, 2017) that cover the entire MY 34 C storm time period, a powerful advantage of multi-spacecraft data assimilation This multi-spacecraft assimilation can be analysed and compared to upper atmosphere Lyman alpha brightness measurements (a proxy for hydrogen escape) from MAVEN/IUVS that display an increase in the Lyman alpha brightness (Chaffin et al, 2021) during the MY 34 C storm. The results are compared to an assimilation during the MY 30 C storm to identify interannual variations in hydrogen escape
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