Multi‐Annual Monitoring of the Water Vapor Vertical Distribution on Mars by SPICAM on Mars Express

• Published in: Journal of geophysical research. Planets 2021-01, Vol.126 (1), p.n/a
• Main Authors: Fedorova, Anna, Montmessin, Franck, Korablev, Oleg, Lefèvre, Franck, Trokhimovskiy, Alexander, Bertaux, Jean‐Loup
• Format: Article
• Language: English
• Subjects: Altitude; Climatology; Dust; Dust storms; High altitude; Hydrogen; Mars; Mars atmosphere; Mars Express (ESA); Mars water; Perihelions; Sciences of the Universe; Seasons; solar occultations; Solstices; Southern Hemisphere; Summer; Summer solstice; Upper atmosphere; Vertical distribution; Water distribution; Water engineering; Water transport; Water vapor
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2020JE006616

The distribution of water vapor with altitude has long remained a missing piece of the observational data set of water vapor on Mars. In this study, we present the first multi‐annual survey of water vapor profile covering the altitude range from 0 to 100 km based on the SPICAM/Mars Express occultation measurements. During the aphelion season, water remains confined below 40–60 km for all Martian years observed. The highest altitude where water vapor can be spotted is between 70 and 90 km during the southern summer (Ls = 240–300°; perihelion season), approaching the transition between the middle and upper atmosphere. In this season, years without a global dust storm (GDS) show a significant moistening of the upper atmosphere (∼100 ppmv) in the southern hemisphere, confirming a seasonal impact on the hydrogen escape rate. The two observed GDS, in MY28 and MY34, show a substantial disparity in water vapor response. The storm in MY28, which coincides with the southern summer solstice, creates the largest excess of water in both hemispheres at >80 km. This climatology of water vapor will supply a robust statistical basis to address the long‐term escape processes of water from Mars. Plain Language Summary The vertical distribution of water vapor in the Martian atmosphere is key to understanding water transport and its escape from the planet, which in turn helps to explain the fate of water through Mars’ history. Recent studies suggest that the transport of water to 80 km can increase the hydrogen escape rate by an order of magnitude and provide evidence for the role of global dust storms (GDS) in the regulation of this process. We monitored the vertical water distribution during multiple Martian years for the first time, including two years with GDSs. We confirm the efficiency of GDS in delivering water to 80 km and emphasize the role of a regular perihelion season, which raises the water in the southern hemisphere every year. The MY28 GDS, coincident with the southern summer solstice, demonstrated the most massive increase of water abundances at high altitudes through the observed years. Key Points Through 8 Martian years observed by SPICAM H2O regularly reaches 40–60 km in the aphelion season and 70–90 km in the perihelion season In southern summer, large H2O vmrs (∼100 ppm) are repeatedly observed up to 80 km, confirming a seasonal impact on the hydrogen escape rate Out of the two observed GDS, in MY28 and MY34, the GDS of MY28, coincident with the southern s