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Y. O. Takahashi, H. Fujiwara, H. Fukunishi (Department of Geophysics, Tohoku University, Japan)
The amplitude of the thermal tides in the Martian atmosphere is very large compared with the case of the terrestrial atmosphere. The effect of the thermal tides on the zonal mean circulation is, therefore, one of the important scientific targets concerning the Martian atmosphere. However, previous studies about this issue have been carried out mainly based on the classical tidal theory. In this study, we have performed two numerical simulations under the perpetual equinox condition using a Mars atmosphere general circulation model. We have also investigated the contribution of thermal tides in the zonal force balance. In the first simulation, we imposed the zonal mean radiative heating rates and the zonal mean surface temperature to exclude thermal tides. On the other hand, the second simulation included thermal tides. Comparing the results of the two simulations, it is found that the meridional circulation generated without thermal tides is much weaker than the case with thermal tides. The estimated residence time of the gstratosphereh (defined as the region above about 20 km) in the case without thermal tides is about 6.5 times as long as that in the case including thermal tides. The significance of thermal tides to drive the meridional circulation can be understood by investigation of the zonal force balance. The Transformed Eulerian Mean diagnostics indicates that Eliassen-Palm (EP) flux divergence due to the diurnal migrating tide plays an important role to maintain the balance among several forces. It is implied that a combination of the large-amplitude of diurnal migrating tide, the vertically distributed dust heating, and the short time constant of the radiative process causes a large EP flux divergence. This result may have important implications as to the underlying environment and the development of planet-encircling dust storms such as an event beginning around the autumnal equinox in 2001.
The author(s) of this abstract have provided an email address for comments about the abstract: yosiyuki@pat.geophys.tohoku.ac.jp