DPS 2001 meeting, November 2001
Session 27. Mars Atmosphere I: Circulation
Oral, Chairs: J. Hollingsworth, A. Toigo, Thursday, November 29, 2001, 10:30am-12:30pm, Regency E

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[27.07] MGS Radio Science measurements of transient eddies on Mars

D. P. Hinson (Stanford Univ.), R. J. Wilson (GFDL/NOAA)

The Sun-synchronous, polar orbit of Mars Global Surveyor (MGS) provides frequent opportunities for radio occultation sounding of the neutral atmosphere. The basic result of each observation is a profile of pressure and temperature versus planetocentric radius and geopotential. More than 4000 profiles were obtained during the 687-day mapping phase of the mission, and additional observations are underway.

These measurements reveal transient eddies (or weather systems) not only in the northern hemisphere but also in the south, where they had not been observed prior to MGS. For example, the traveling eddies that appear in midwinter (Ls=134\deg--148\deg) at 67\deg--70\degS have a period of ~2 days, a zonal wavenumber s=3, and a peak amplitude of ~7 K at the 300-Pa pressure level. The measured zonal variations in geopotential height imply that the meridional winds have an amplitude of 10--15 m s-1. Strong zonal variations in eddy amplitude signal the presence of a possible ``storm zone'' at 150\deg--330\degE longitude. The minimum temperature associated with the eddies is ~2 K colder than saturation of CO2, close to the threshold where nucleation and condensation of new ice particles can occur. These eddies are relatively shallow, with temperature variations confined to pressures greater than ~50 Pa. A simulation by a Mars general circulation model (MGCM) produces traveling eddies that closely resemble the observations. We are currently using the MGCM to gain a deeper understanding or their behavior. This talk will also include examples of traveling eddies in the northern hemisphere.

Funding for this work was provided by the MGS Project and the NASA Mars Data Analysis Program.

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