Cloud-tracked winds for the first Mars Global Surveyor mapping year

Abstract

We have measured winds using cloud motion in consecutive Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) wide-angle global map swaths taken during the first mapping year (L s 135°–360°–111°). We present a total of ∼11,200 wind vectors collected in the north polar region during L_s 135°–195° (late summer/early fall) and L_s 20°–55° (mid spring) and in the south polar region during L_s 337°–10° (late summer/early fall). For cases with good coverage, we also present the derived mean zonal and meridional winds and the associated eddies. The speed of the zonal winds in 60°N–70°N increases at ∼0.6 m/s/°L_s in late northern summer, and that in 60°S–70°S increases at a rate of ∼0.7 m/s/°L_s in late southern summer. The latitudinal distribution of zonal wind within 50°N–75°N from mid northern summer to early northern fall indicates that winds at higher latitudes are generally weaker than those at lower latitudes, but the rate of increase with time is faster at higher latitudes. There is a cyclonic gyre in the 90°W–0°–30°E sector in the north polar region. There are large-scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the north polar region from mid to late summer. The cloud-tracked winds in the north are generally consistent with winds calculated by general circulation model at the water condensation level derived from MGS Thermal Emission Spectrometer (TES) observations but appear stronger than the gradient winds derived from TES assuming no flow at the surface.