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A Martian General Circulation Experiment with Large Topography

James B. PollackNASA Ames Research Center, Mountain View, CA 94035

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Conway B. LeovyDepartment of Atmospheric Sciences, University of Washington, Seattle 98195

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Paul W. GreimanDepartment of Meteorology, Florida State University, Tallahassee 32306

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Yale MintzLaboratory for Atmospheric Sciences, NASA Goddard Space Flight Center, Greenbelt, MD 20771

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Abstract

A three-layer general circulation model, used to simulate the Martian atmosphere, is described and results are presented. The model assumes a dust-free pure C02 atmosphere and allows for a diurnally- varying convective boundary layer. Smoothed Martian topography and albedo variations are incorporated. The simulation described is for the period near southern winter solstice, season of the Viking landings. The zonally-averaged circulation, mass, heat and momentum balances, and properties of stationary and transient waves are described in some detail, and are compared with results of previous simulations of the Martian general circulation, with related features of the Earth's general circulation, and with observed characteristics of the Martian atmosphere.

The principal conclusions are the following: 1) The simulated zonally-averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of Leovy and Mintz (1969), and compares reasonably well with observations, except for differences attributable to dust and season. 2) The meridional mass flow produced by the seasonal condensation of CO2, in the winter polar region has a major influence on the circulation, but, because of the weak influence of atmospheric heat transport, it is controlled almost entirely by radiation. 3) Quasi-barotropic stationary waves forced kinematically by the topography and resembling topographically-forced terrestrial planetary waves, are generated by the model in the winter hemisphere region of strong eastward flow, while baroclinic stationary waves are thermally forced by topography in the tropics and summer subtropics. 4) Transient baroclinically unstable waves, of somewhat lower dominant wavenumber than those found on the Earth, are generated in winter midlatitudes and their amplitudes, wavenumbers and phase speeds closely agree with what has been deduced from the Viking lander observations.

Abstract

A three-layer general circulation model, used to simulate the Martian atmosphere, is described and results are presented. The model assumes a dust-free pure C02 atmosphere and allows for a diurnally- varying convective boundary layer. Smoothed Martian topography and albedo variations are incorporated. The simulation described is for the period near southern winter solstice, season of the Viking landings. The zonally-averaged circulation, mass, heat and momentum balances, and properties of stationary and transient waves are described in some detail, and are compared with results of previous simulations of the Martian general circulation, with related features of the Earth's general circulation, and with observed characteristics of the Martian atmosphere.

The principal conclusions are the following: 1) The simulated zonally-averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of Leovy and Mintz (1969), and compares reasonably well with observations, except for differences attributable to dust and season. 2) The meridional mass flow produced by the seasonal condensation of CO2, in the winter polar region has a major influence on the circulation, but, because of the weak influence of atmospheric heat transport, it is controlled almost entirely by radiation. 3) Quasi-barotropic stationary waves forced kinematically by the topography and resembling topographically-forced terrestrial planetary waves, are generated by the model in the winter hemisphere region of strong eastward flow, while baroclinic stationary waves are thermally forced by topography in the tropics and summer subtropics. 4) Transient baroclinically unstable waves, of somewhat lower dominant wavenumber than those found on the Earth, are generated in winter midlatitudes and their amplitudes, wavenumbers and phase speeds closely agree with what has been deduced from the Viking lander observations.

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