A Study of Propagation of Nonlinear Acoustic-Gravity Waves in the Middle and Upper Atmosphere by Means of Numerical Modeling

摘要

A numerical model of the vertical propagation and decay of nonlinear acoustic-gravity waves (AGW) from the Earth surface to the upper atmosphere is described. Monochromatic vertical velocity variations at the Earth surface are used as the AGW source in the model. The numerical method for solving threedimensional hydrodynamic equations is based on finite-difference representation of the fundamental laws of conservation, which makes it possible to calculate not only smooth, but also physically correct generalized solutions of the hydrodynamic equations. The equations are solved in a range of altitudes from the ground up to 500 km. The background temperature, density, molecular viscosity and thermal conductivity coefficient are specified according to standard atmosphere models. The dependence of the characteristics of the waves on the amplitude of the wave source at the lower boundary is examined. The amplitudes of the AGW increase with the altitude, and the waves can break down due to nonlinear effects in the middle and upper atmosphere, depending on the amplitude of the source.