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A.F.C. Bridger (San Jose State University/NASA Ames), R.M. Haberle, J. Schaeffer (NASA Ames Research Center)
The role of tides in Mars' atmosphere is examined via simulations with a comprehensive Mars General Circulation Model (the NASA-Ames MGCM). We examine two annual simulations of the atmosphere. The first includes all physics typically included in such models (including MOLA topography to define the lower boundary condition, and assuming a constant dust opacity of 0.3). In the second simulation, diurnally-averaged heating is assumed, thus switching off the forcing mechanism behind the classical, sun-synchronous tides.
Tidal amplitudes in Earth's lower and middle atmosphere are relatively small compared to other oscillations (e.g., when compared to the surface pressure signals of midlatitude baroclinic waves), and thus tides have often been neglected in efforts to understand the dynamics of Earth's lower and middle atmosphere. However, tides in Mars' atmosphere have higher relative amplitudes (especially in dusty conditions). Thus, they may be expected to have a greater impact on the structure and behavior of Mars' atmosphere. These impacts are investigated here.
We focus here on time- and zonally-averaged features of the circulation as they vary throughout the year. Specifically, we look at the zonally-averaged circulation (zonal wind and overturning circulation), and at the structural properties of stationary planetary waves, and at how these structures change with the exclusion of tides. Results are presented for various seasons. Some diagnostics may be presented to aid in the interpretation of differences found.