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 (Ls = 134 –148 ) through analysis of radio occultation measurements at 67 –70 S 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 150 –330 E longitude. Within this longitude band the eddies achieve peak amplitudes at the 300-Pa pressure level of 7 K in temperature and 10–15 m s 1 in meridional wind speed. The minimum temperature associated with the eddies is 2 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.