Influence of Mean Zonal Motion and Meridional Temperature Gradients on the Solar Semidiurnal Atmospheric Tide: A Spectral Study. Part II: Numerical Results

Abstract

Classical and nonclassical model calculations have been performed for the solar semidiurnal tidal oscillations in the earth's atmosphere, for prescribed basic-state parameters and heating functions appropriate for the solstitial seasons when the nonclassical effects associated with the mean zonal wind are expected to be maximum. It is found that the enrichment of the higher order spectral components characteristic of the nonclassical model is due to the cross-coupling rather than the self-coupling of the spectral components in the model. These cross-coupling effects are shown to be sufficiently well represented by a mode-coupling model described in Section 3 of Part I. As explained in Part I, the effect of cross-coupling may be considered as some kind of indirect forcing. Such indirect forcing, which can be applied either at the lower boundary or inside the medium, is obtained and compared for each spectral component with the direct thermal forcing. It is demonstrated that the actual behavior of a particular spectral component (such as the m=4 component whose enrichment is an important aspect of the nonclassical model) in the progressive wave regime (where waves forced from below dominate) can be explained as the net result of forcings, both direct and indirect, at the lower boundary and from different altitude regions above. Results of our model calculations for wind, temperature and pressure oscillations are compared with available observations at various altitudes. While this comparison succeeds in exposing definite nonclassical influences in the observations, it also reveals significant inadequacies of our model.