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J.R. Barnes, M. Matheson (Oregon State U.)
Previous GCM simulations have shown that the intensity of transient baroclinic eddy activity in middle latitudes in southern winter is much weaker than that in northern winter. Sensitivity experiments have demonstrated that this basic hemispheric asymmetry in the Martian atmospheric circulation is partly due to differences in the large topography between the two hemispheres. However, it is also partly due to the basic asymmetry in the thermal forcing of the atmosphere at the solstice seasons. Numerical studies have been carried out using a simplified GCM (SGCM) to investigate the impact of the basic thermal forcing asymmetry on the baroclinic eddies, in the absence of topographic effects. The results of the SGCM experiments indicate that the baroclinic eddies in the Martian atmosphere are extremely sensitive to the magnitude of the midlatitude north-south temperature gradients. Relatively small increases in the gradients produce relatively large increases in the intensity of the baroclinic eddy activity. The SGCM results indicate that the bulk of the difference in strength between the baroclinic eddies in the north and south can be explained by the basic thermal forcing asymmetry that exists in the current epoch. The characteristic differences in atmospheric dust loading between northern and southern winters would be expected to further enhance the asymmetry in the eddy activity, since increased dustiness tends to increase the winter midlatitude temperature gradients. Topographic effects act to further enhance the hemispheric asymmetry in the baroclinic eddy activity, which may have important implications for the current climate system of Mars. This work was supported by a grant from the NASA Planetary Atmospheres Program.
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