Excitation of gravity modes in the parameter space of the tidal wind system

Perturbing the Navier-Stokes equation in the ionospheric F-region, the disp ersion relation and the unstable regions in wavenumber space are derived as a function of two control parameters, the colatitude theta and the slow ti me evolution for tidal modes tau. Our results satisfy the internal gravity wave (IGW) dispersion relation and are in good agreement with observational data. Also, we obtained a nice prediction for the excitation regions of th ese modes in the parameter space (theta, tau). The distribution of IGW exci tations, in this parameter space is in very good agreement with observation al data distributed along the day. An alternative explanation to the disapp earence of IGW near the equator is given. Our model predicts an interesting latitude dependence, which needs to be tested by new observational data.