General circulation modeling of the Martian upper atmosphere during global dust storms

Simulations with a general circulation model (GCM) have been performed to study the Martian upper atmosphere during two major dust storms. The GCM extending from the surface to about 160km included a spectral parameterization of subgrid-scale gravity waves suitable for planetary thermospheres, and prescribed four-dimensional dust distributions corresponding to storm events near the equinox and solstice (Martian years 25 and 28, respectively). The results show that the wind and temperature fields in the upper atmosphere above approximate to 100km respond to such storms as intensively as in the lower atmosphere. During the equinoctial storm, the temperature above the mesopause dropped by up to 30K everywhere except in the Northern Hemisphere high latitudes, where it rose by up to 15K. At the solstitial storm, the temperature above the mesopause decreased by up to 40K in the winter hemisphere, by 15 K in the summer hemisphere, and increased by 30-40K in tropics and in the summer hemisphere above 130km. Prograde and retrograde zonal wind jets intensified throughout the atmosphere at all heights and during both dust scenarios. These changes are the result of the altered meridional overturning circulation induced by resolved and unresolved waves. Atmospheric density during dust storms enhanced in average by a factor of 2 to 3 in the mesosphere and lower thermosphere, which agrees well with observations.