MGS TES observations of the water vapor in the martian southern polar atmosphere during spring and summer

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2019-10, Vol.331, p.26-48
• Main Authors: Pankine, Alexey A., Tamppari, Leslie K.
• Format: Article
• Language: English
• Subjects: Atmospheres, dynamics; Mars; Mars, atmosphere; Mars, climate; Mars, polar caps
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2019.05.010

We report retrievals of atmospheric water vapor abundances in and around the South Polar Region (SPR) of Mars during spring and summer of Mars Years (MY) 24–26 (1999–2003). The retrieval utilizes infrared spectra collected by the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor (MGS) spacecraft. Modifications to the existing retrieval algorithm enable the first retrievals of water vapor abundances over regions covered by the seasonal CO2 frost during spring. We present polar maps of water vapor variability in the SPR for the time periods Ls = 195°–345° in MY24–26. Water vapor behavior in the SPR in MY24 and MY26 exhibits substantial similarity in spatial distribution for the same dates and in temporal variability. Water vapor behavior in MY25 is significantly different from that in MY24 and MY26 with abundances ~30% lower around summer solstice (Ls = 270°). We hypothesize that water vapor behavior in MY25 was affected by the Global Dust Storm (GDS) that started at Ls ~185° of that year and significantly affected the atmosphere of the whole planet. We speculate that the reduction in the observed vapor abundances in MY25 could have resulted from disruption of the southward atmospheric vapor transport from mid-latitudes by the GDS or from reduction of the rate of desorption of vapor from thawed circumpolar terrains due to changes in surface temperature during the GDS. Through most of the spring, highest vapor abundances are observed just northward of the retreating edge of the seasonal CO2 cap, with generally low abundances over the seasonal cap. Repeated cycles of condensation and re-sublimation of water vapor on the edge of the retreating cap could be responsible for this build-up of vapor near the cap edge. Relatively high vapor abundances that are systematically observed over some regions of the cap in late spring could be associated with venting of the mixture of water vapor, CO2 gas and dust from underneath the seasonal cap through fractures in the frost. We explore the evolution of the water vapor in the SPR during spring and summer using two 1-dimenional models representing two limiting cases that attribute observed changes to either atmospheric transport or surface sources. The atmospheric transport model appears to be more consistent with observations, suggesting that atmospheric transport plays the dominant role in the water vapor cycle in the SPR. However, activity of surface processes such as desorption of vapor from the regoli