The focus of this project is to provide support for the Mars Global Surveyor (MGS) spacecraft aerobraking maneuver using a global atmospheric circulation model. After modifications are completed which will raise the NASA/Ames Mars general circulation model' s (MGCM) vertical extent to 100-120 km above the planet' s surface, the primary goal of this project will be to determine plausible spatial and temporal variability of high-level atmospheric density at the seasonal date of the MGS orbital aerobraking transition. This effort will aid in the determination of a range of course correction strategies during the MGS 100-day orbit circularization maneuver. A secondary task will be to isolate the effects of a breaking gravity-wave parameterization scheme recently included into the MGCM. The dynamical importance associated with gravity wave momentum flux deposition within high regions of the planet' s atmosphere and its net effect on the planet's circulation will be determined. In addition, using a quasi-geostrophic parameterization of planetary (Rossby) wave breaking together with results from the MGCM, a diagnostic assessment of the importance of breaking planetary waves in Mars' middle atmosphere will be carried out. In particular, a Rossby wave breaking criterion and an associated dissipation rate will be assessed. Following such improvements in the MGCM' s high-level simulation capability, and careful analyses of the atmospheric circulation in middle and high levels, a final task will be to provide a coupling (i.e., lower boundary condition) to a separate (independent) Mars thermospheric circulation model.