Transient eddies in the southern hemisphere of Mars

[1] Mars Global Surveyor is providing the first observations of transient eddies in the southern hemisphere of Mars. We derive basic properties of the traveling eddies that appear in midwinter (L-s = 134degrees-148degrees) through analysis of radio occultation measurements at 67degrees-70degreesS latitude. The dominant mode has a period of 2 solar days and a zonal wavenumber s = 3. Strong zonal variations in eddy amplitude signal the presence of a possible "storm zone'' at 150degrees-330degreesE longitude. Within this longitude band the eddies achieve peak amplitudes at the 300-Pa pressure level of similar to7 K in temperature and 10-15 m s(-1) in meridional wind speed. The minimum temperature associated with the eddies is similar to2 K colder than saturation of CO2, close to the threshold where nucleation and growth of new ice particles can occur. A simulation by a Mars general circulation model produces traveling eddies that closely resemble the observations.