Transient eddies in the southern hemisphere of Mars

Abstract

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 ms-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.