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Estimation of changes in the composition of the Martian atmosphere caused by CO 2 condensation from GRS Ar measurements and its application to the rederivation of MGS radio occultation measurements
Author(s) -
Noguchi K.,
Ikeda S.,
Kuroda T.,
Tellmann S.,
Pätzold M.
Publication year - 2014
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2014je004629
Subject(s) - mixing ratio , atmosphere (unit) , atmosphere of mars , polar , martian , mars exploration program , radio occultation , atmospheric sciences , occultation , supersaturation , environmental science , chemistry , ionosphere , geology , astrobiology , physics , astrophysics , meteorology , geophysics , astronomy , organic chemistry
We propose a method to estimate seasonal changes in the composition of the Martian atmosphere, which is influenced by CO 2 condensation due to the polar nights at southern high latitudes. The method relies on measurements of the Ar concentration obtained by the Gamma Ray Spectrometer (GRS) onboard Mars Odyssey. We assume that the Martian atmosphere is composed of CO 2 , N 2 , and Ar, and is vertically well mixed. Since N 2 and Ar do not condense even during the polar nights, the ratio of N 2 and Ar remains constant, and the concentrations of N 2 and CO 2 can be estimated from Ar measurements. Estimates of the atmospheric composition were utilized for the rederivation of temperature and pressure profiles in the Mars Global Surveyor (MGS) radio occultation measurements (∼70 profiles of ∼20,000 profiles in the whole data set) at southern polar latitudes (90°S–75°S) during the autumn, winter, and spring seasons ( L s = 0°–240°). The rederived profiles indicated that use of the standard global composition overestimated the temperature by at least approximately 5 K at L s = ∼120° (midwinter), when the largest CO 2 depletion occurred and the CO 2 volume mixing ratio fell to 78%. The occurrence and degree of CO 2 supersaturation were several times higher and larger, respectively, in the rederived temperature profiles than in the original MGS profiles. This suggests that consideration of CO 2 depletion during southern polar nights is needed when studying CO 2 supersaturation using radio occultation profiles.