An Analysis of the Effect of Topography on the Martian Hadley Cells

Previous work with Mars general circulation models (MGCMs) has shown that the north south slope in Martian topography causes asymmetries in the Hadley cells at equinox and in the annual average. To quantitatively solve for the latitude of the dividing streamline and poleward boundaries of the cells, the Hadley cell model of Lindzen and Hou was modified to include topography. The model was thermally forced by Newtonian relaxation to an equilibrium temperature profile calculated with daily averaged solar forcing at constant season. Two sets of equilibrium temperatures were considered that either contained the effects of convection or did not. When convective effects were allowed, the presence of the slope component shifted the dividing streamline upslope, qualitatively similar to a change in season in Lindzen and Hou's original (flat) model. The modified model also confirmed that the geometrical effects of the slope are much smaller than the thermal effects of the slope on the radiative convective equilibrium temperature aloft. The results are compared to a simple MGCM forced by Newtonian relaxation to the same equilibrium temperature profiles, and the two models agree except at the winter pole near solstice. The simple MGCM results for radiative convective forcing also show an asymmetry between the strengths of the Hadley cells at the northern summer and northern winter solstices. The Hadley cell weakens with increasing slope steepness at northern summer solstice but has little effect on the strength at northern winter solstice.