Interannual similarity and variation in seasonal circulation of Mars' atmospheric Ar as seen by the Gamma Ray Spectrometer on Mars Odyssey

Ann L. Sprague, William V. Boynton, Francois Forget, Yuan Lian, Mark Richardson, Richard Starr, Albert E. Metzger, David Hamara, Thanasis Economou

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15 Scopus citations


More than 3 Mars' years (MY) of atmospheric argon (Ar) measurements are used to study annual and seasonal variations in atmospheric transport and mixing. Data are obtained over the period 20 May 2002 to 4 May 2008 by the Gamma Subsystem (GS) of the Gamma Ray Spectrometer (GRS) on the Mars Odyssey spacecraft in orbit around Mars. Here we augment previous studies of Mars' Ar in which strong seasonal variations were observed and horizontal meridional mixing coefficients for the southern hemisphere were computed. Comparison of year-to-year seasonal abundance shows strong similarity but also some short-period (∼15-30 Ls) and interannual variations. Evidence for short periods of strong eddy transport is exhibited during autumn and winter. The seasonal change in Ar concentration for southern latitudes is relatively gradual and well defined, but seasonal changes at high northern latitudes are chaotic and indicate that atmospheric disturbance is ubiquitous. Major topographic landforms (Elysium, Tharsis, Noachis Terra, Hellas) apparently have little control over seasonal Ar concentration at the spatial resolution of the GRS data set. Some indication of local enhanced Ar concentration is present from 30N to 60N for the Hellas and Tharsis sectors in late winter and early spring. The data show some significant (3) differences between MY 26 and MY 27 in geographical sectors that are likely produced by local weather. The GS data do not show seasonal variation of Ar at equatorial and low-latitude zones, in contrast to those from the Alpha Particle X-ray Spectrometer (APXS) measurements from the Mars Exploration Rovers.

Original languageEnglish (US)
Article numberE04005
JournalJournal of Geophysical Research: Planets
Issue number4
StatePublished - 2012
Externally publishedYes

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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