Mars atmospheric dynamics as simulated by the NASA Ames general circulation model .3. Winter quasi-stationary eddies

A set of simulations with the NASA Ames Mars general circulation model (GCM) has been analyzed to define the basic properties and dynamics of quasi-stationary eddy circulations in the winter hemisphere. These circulations, differing substantially from those in low latitudes and the summer hemisphere, extend from the surface to the model top at similar to 47 km; typically, the largest geopotential and wind perturbations are found at the highest model level. Near the surface the eddies are of largest amplitude in lower latitudes, but above similar to 5-10 km the amplitudes are a maximum in middle and high latitudes. The vertical structure of the eddies is nearly equivalent barotropic; the phase variation in latitude is also relatively small. Zonal wavenumbers 1 and 2 dominate the stationary circulations, with wave 3 being of significance only at low levels (below similar to 10 km). The quasi-stationary eddies differ substantially in northern and southern winters, and undergo considerable changes with increasing dustiness in northern winter. The southern winter eddy circulation is dominated by zonal wavenumber 1, while the northern eddies have a strong wavenumber 2 component at low levels of dust loading; at high dust levels wavenumber 1 becomes dominant. This change may be at least partly the result of the dusty zonal-mean state becoming more responsive to wave 1 forcing. The standing eddies in a GCM simulation for L(s) similar to 0 degrees exhibit considerable similarity in basic structure and amplitude to those revealed by a recent analysis of Viking IRTM data [Banfield et al., 1996], though there are differences in the phases of the eddy patterns.