Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0309z&link_type=abstract
American Astronomical Society, DPS meeting #40, #3.09; Bulletin of the American Astronomical Society, Vol. 40, p.391
Astronomy and Astrophysics
Astronomy
Scientific paper
Two recent studies, Richardson and Wilson 2002 (Nature 416, 298) and Takahashi et al. 2003 (J. Geophys. Res. 108, 5018), have shown that the north-south slope in the zonally averaged Martian topography is related to the asymmetry of the Hadley cells about the equator observed in Martian atmospheric General Circulation Models (GCMs). To determine the connection between the height of the surface and the atmospheric circulation, a Martian version of the MIT atmospheric GCM was used to run experiments that were forced using Newtonian relaxation to two different radiative equilibrium states. The first state, referred to as pure radiative equilibrium, is a two-stream radiative transfer model that assumes the Eddington approximation, a gray atmosphere at long wavelengths, and no solar absorption in the atmosphere. The GCM results show little difference in the strength and extent of the Hadley cells with and without topography when forced with this case. The second state, radiative-convective equilibrium, assumes that the discontinuity between the surface and the atmosphere directly above the surface that exists in the pure radiative equilibrium model is resolved through convection, so that the temperature follows an adiabat in the convective layer and is in pure radiative equilibrium elsewhere. GCM runs using this radiative equilibrium state show a change when topography is added, which is qualitatively similar to the previous studies mentioned above. In the radiative-convective equilibrium model, the temperature aloft depends on the height of the surface below, such that the temperature at a given pressure level aloft is warmer over an elevated surface than over a lower surface. The topography shifts the latitude of maximum temperature in much the same way that a change of season does, for which current theories of the Hadley circulation already exist (e.g. Lindzen and Hou 1988, J. Atmos Sci. 45, 2416).
Plumb Alan R.
Wilson Richard J.
Zalucha Angela M.
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