A Numerical Circulation Model with Topography for the Martian Southern Hemisphere

Clifford Mass Laboratory for Planetary Studies, Cornell University, Ithaca, N. Y. 14853

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Carl Sagan Laboratory for Planetary Studies, Cornell University, Ithaca, N. Y. 14853

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Abstract

A quasi-geostrophic numerical model, including friction, radiation and the observed planetary topography is applied to the general circulation of the Martian atmosphere in the Southern Hemisphere at latitudes south of about −35°. Near-equilibrium weather systems developed after about 5 model days. To avoid violating the quasi-geostrophic approximation, only 0.8 of the already smoothed relief was employed. Weather systems and velocity fields are strikingly tied to topography. A 2 mb middle-latitude jet stream is found of remarkably terrestrial aspect. Highest surface velocities, both horizontal and vertical, are predicted in western Hellas Planitia and eastern Argyre Planitia, which are common sites of orgin of major Martian dust storms. Mean horizontal velocities >30 m s−1 and mean vertical velocities >0.2 m s are sometimes found just above the surface velocity boundary layer, apart from eddy velocity contributions. When consideration is taken of scaling to full topography and the probable gustiness of Martian winds, it seems very likely that the general circulation is adequate, at certain times and places, to transport dust from the surface of Mars, as observed. Certain sources and sinks of vertical dust streaming are suggested; the entire south circumpolar zone appears to be a dust sink in winter.

Abstract

A quasi-geostrophic numerical model, including friction, radiation and the observed planetary topography is applied to the general circulation of the Martian atmosphere in the Southern Hemisphere at latitudes south of about −35°. Near-equilibrium weather systems developed after about 5 model days. To avoid violating the quasi-geostrophic approximation, only 0.8 of the already smoothed relief was employed. Weather systems and velocity fields are strikingly tied to topography. A 2 mb middle-latitude jet stream is found of remarkably terrestrial aspect. Highest surface velocities, both horizontal and vertical, are predicted in western Hellas Planitia and eastern Argyre Planitia, which are common sites of orgin of major Martian dust storms. Mean horizontal velocities >30 m s−1 and mean vertical velocities >0.2 m s are sometimes found just above the surface velocity boundary layer, apart from eddy velocity contributions. When consideration is taken of scaling to full topography and the probable gustiness of Martian winds, it seems very likely that the general circulation is adequate, at certain times and places, to transport dust from the surface of Mars, as observed. Certain sources and sinks of vertical dust streaming are suggested; the entire south circumpolar zone appears to be a dust sink in winter.

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