Modeling the passage of large-scale internal gravitational waves from the troposphere to the ionosphere

On the basis of two-dimensional numerical computations of the trajectories of internal gravitational waves (IGW), propagation of IGW in a vertically non-uniform atmosphere from tropospheric heights to the ionosphere is considered in the presence of zonal flows with allowance for their height heterogeneity. In the troposphere, IGW can be excited with the development of such processes as large-scale vortices, earthquakes, etc. For series of data on the vertical profiles of the Väisälä-Brent frequency and the altitude profile of the velocity of the zonal flow in the atmosphere, an analysis is made for the possibility of passage of small- and medium-scale IGW from the troposphere to the ionosphere up to a height of more than 80 km. According to numerical calculations, depending on the IGW parameters and the zonal flow in the atmosphere, various variants of IGW propagation in a vertically inhomogeneous troposphere-ionosphere system are possible. In particular, a conclusion made earlier is confirmed that if there are critical layers or layers of vertical refection in the atmosphere, the passage of IGW into the ionosphere is impossible. In the presence of a critical layer, IGW propagating to it from below greatly slows down, the vertical component of the wave vector increases strongly, and the IGW near the critical layer propagates almost horizontally. Moreover, due to the large increase in viscosity, it is actually completely absorbed at the height of the critical layer. Depending on the initial parameters of the system, there may be a situation when a layer of horizontal refection appears at a certain height, and IGW is refected (propagating upward) back to the source of its excitation. Then, a vertical refection layer can appear above, and the wave, propagating downward from it, again approaches the horizontal refection layer. After refection in it, IGW returns to the source on the other side. According to the numerical calculations of the IGW dynamics, the horizontal displacement of the IGW packet during propagation from the troposphere to the ionosphere can be large (depending on the choice of the initial parameters of the problem, the altitude profles of the zonal stream, the Väisälä-Brent frequency) and can be thousands of kilometers. Consequently, under the conditions of realization of the IGW passage from the troposphere to ionospheric heights, precursors of crisis events in the ionosphere (including plasma perturbations) can be observed by satellite equipment at large distances horizontally from the source of generation of IGW. This circumstance should be taken into account when analyzing and interpreting experimental data on the relationship between ionospheric disturbances and crisis phenomena, for example, earthquakes, tropical cyclones, etc.