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J. M. Forbes (University of Colorado)
Large stationary planetary waves (zonal wavenumbers s=1 and s=2) have been observed in the lower thermosphere of Mars by the MGS accelerometer experiment (Keating et al., 1998). These measurements motivate the current work, which focuses on the mechanisms responsible for thermospheric penetration and inter-hemispheric coupling of planetary waves in the Mars atmosphere. A linear viscous wave model is used to obtain the stationary wave solutions in a spherical atmosphere extending from the ground to ~300 km. The solutions represent perturbations on a latitude-height dependent zonal mean state which must be specified a priori, along with the thermal and topographic forcing of the planetary waves. The model is a newly-developed Mars version of the terrestrial Global Scale Wave Model (GSWM), or MGSWM. Results from several numerical experiments with the MGSWM are presented, highlighting the effects of mean zonal winds and interactions with gravity waves on the thermospheric penetration of stationary planetary waves. The latter hold the greatest promise for explanation of the MGS accelerometer measurements, by virtue of the planetary wave modulation of molecular dissipation of gravity waves, which deposit mean momentum and heat into the Martian lower thermosphere.