A Martian General Circulation Experiment with Large Topography

A three-layer general circulation model, used to simulate the Mars atmosphere, is described and results are presented. The model assumes a dust-free, pure CO sub(2) atmosphere and permits a diurnally varying convective boundary layer. Smoothed Mars 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 and are compared with results of previous simulations of the Mars general circulation, with related features of the Earth's general circulation, and with observed characteristics of the Mars atmosphere. The principal conclusions are given. 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 CO sub(2) 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, whereas baroclinic stationary waves are thermally forced by topography in the Tropics and summer subtropics. 4) Transient baroclinically unstable waves, of lower dominant wavenumber than those found on the Earth, are generated in winter midlatitudes, and their amplitudes, wavenumbers, and phase speeds closely agree with information deduced from the Viking lander observations.