Abstract
A nonlinear, 3D, time dependent numerical spectral model (NSM) is discussed, extending from the ground up into the thermosphere. The NSM incorporates the Doppler spread parameterization (DSP) for small scale gravity waves (GW) developed by Hines and is applied in a study of the diurnal tides and the mean zonal circulation, interacting self consistently. Our model results lead to the following conclusions: (1) Due to absorption of GW momentum in the regime of increasing horizontal winds, the amplitude of the fundamental diurnal tide is amplified at altitudes between 80 and 120 km. (2) The semidiurnal tide is also amplified in this way when it is excited without the diurnal tide. With the diurnal tide, however, the amplitude of the semidiurnal tide is reduced. Wave filtering causes strong nonlinear coupling between the two tidal components. (3) The annual variation in the zonal circulation causes GW filtering to produce a strong semiannual variation in the diurnal tide, which is observed on UARS. (4) Preliminary results show large seasonal modulations of the semidiurnal tide that appear in part to be caused by GW filtering associated with the seasonal variations in the diurnal tide. (5) The tides are modulated with periods that are related to the planetary waves that are generated by dynamical processes in the mesosphere.
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