Features of the Supersonic Gravity Wave Penetration from the Earth’s Surface to the Upper Atmosphere

Using a high-resolution numerical model, we simulate the gravity wave (GW) modes having supersonic horizontal phase velocities on the Earth’s surface and propagating to the upper atmosphere. Such GWs can be produced, for example, by low-frequency spectral components of the seismic waves propagating over the Earth’s crust surface with horizontal velocities of up to a few kilometers per second. According to the linear theory, GW modes with so high horizontal velocities should be trapped, with their amplitudes exponentially decreasing with the altitude. Numerical experiments with a nonlinear wave model showed that the initial acoustic–gravity wave pulse occurring when a non-stationary ground wave source is “switched on” can create a system of relatively slow moving mesoscale irregularities at altitudes from the Earth’s surface to the upper atmosphere. The trapped GW modes excited by a supersonic surface source may feed this system of irregularities with energy and ensure its existence within time intervals of up to tens of wave periods. The irregularities can form undulatory inclined wave fronts, similar to effective upward propagating GWs. Thus, the supersonic trapped modes excited on the Earth’s surface can create atmospheric internal GWs having subsonic horizontal phase velocities and spreading to high altitudes.