Diurnal Winds Near the Martian Polar Caps

Abstract

Large, diurnally varying surface temperature gradients occur at the polar cap periphery during Martian spring and summer. A primitive equation numerical model having grid points lying in the meridional plane is developed to calculate the wind field in this intensely baroclinic region. The atmosphere is assumed at rest initially, with the developing circulation being driven solely by the oscillating surface temperature gradient. Maximum winds of approximately 20 m s?1 develop when the atmosphere is initially isothermal. Model sensitivity to surface boundary layer depth is examined, while in other experiments the initial lapse rate is varied. Heating rates due to planetary radiation, though large, are found to have a negligible influence upon the flow. Convective heat transfer is the dominant diabatic process. Bagnold's (1941) theory of sand-grain movement, adapted to Martian surface conditions, is utilized to investigate the dust-lifting potential of the polar winds. As modelled, the surface wind stresses appear insufficient to raise dust, but this conclusion could be altered with inclusion of additional physical processes in the model.