Excitation of gravity modes in the parameter space of the tidal wind system (II): magnetic effects

The Navier-Stokes, continuity and energy balance equations including magnet ic effects for an inviscid compressible fluid in the ionospheric F-region w ere perturbed around the tidal phenomenological solution. We imposed adiaba ticity and incompressibility to the perturbation. Our results satisfy the i nternal gravity wave (IGW) dispersion relation. The stable and unstable reg ions of these modes were derived as a function of two control parameters, t he colatitude theta and the slow time evolution for tidal modes tau. These regions were obtained for different values of the magnetic field intensity, showing good agreement with observational data for the South Atlantic anom aly. Our model predictions for other magnetic field intensities correspondi ng to other latitude dependences need to be contrasted with new observation al data. In addition we show for some hours and latitudes that, resonant in teraction occurs between low frequency tidal waves and two high frequency g ravity waves. In these regions, where tidal modes are linearly unstable, th e gravity group velocity is modulated by a function of the tidal phase velo city.