Observed Strong Enhancements of N2 and Ar Test New Theories of the Dynamics of Mars Polar Atmosphere

Details Observed Strong Enhancements of N2 and Ar Test New Theories of the Dynamics of Mars Polar Atmosphere Observed Strong Enhancements of N2 and Ar Test New Theories of the Dynamics of Mars Polar Atmosphere

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53a..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P53A-04

Physics

[0300] Atmospheric Composition And Structure, [0343] Atmospheric Composition And Structure / Planetary Atmospheres, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Data acquired by the Gamma Subsystem (GS) and Neutron Spectrometer (NS), two components of the Gamma Ray Spectrometer (GRS) suite of instruments currently operating on the Mars Odyssey spacecraft in orbit around Mars, have revealed up to a factor of six enhancement in atmospheric N2 and Ar over south polar regions during southern winter. The enhancement is repeated year to year. Argon and N2, along with CO and CH4, are gasses that do not condense at Mars temperatures and are thus called "noncondensables" with respect to Mars atmospheric composition and dynamics. Argon and N2 begin to accumulate over the southern pole in mid-autumn, reach a maximum by early winter, and then rapidly diminish in concentration before the formation of the seasonal CO2 cap is completed. These results have challenged basic assumptions underlying calculations of Mars atmospheric circulation and dynamics with Global Circulation Models (GCMs), resulting in the development of improved models. Three modifications that have resulted in a better match to the observed Ar and N2 concentrations in the south polar region are the inclusion of convective available potential energy that can induce vigorous convective mixing, modification of high latitude atmospheric pressures, and inclusion of detailed microphysical processes. These improvements mark a step forward in GCM modeling which will be needed in order to understand martian climate history. Mars atmospheric Ar is measured (using the GS) by the integration of a 1294 keV gamma-ray line generated by the decay of 41Ar created when a thermal neutron is captured by 40Ar in Mars atmosphere. The combined inventory of N2 and Ar is determined (using the NS) along with the column abundance of seasonal CO2 surface ice from thermal and epithermal neutron counting rates. Nearly three full Mars' years atmospheric N2 and Ar measurements (8 June 2002 to 22 March 2006) are used to study annual and seasonal variations in atmospheric transport and mixing. Remarkable agreement in the timing of accumulation and depletion of N2 and Ar in both data sets provides strong evidence for the timing of the formation and break up of the southern polar vortex and for year to year variations in south polar atmosphere dynamics.

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