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

Abstract

AbstractThe 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.