Reflectionless propagation of acoustic waves through the Earth’s atmosphere

The vertical propagation of acoustic waves in the inhomogeneous compressible atmosphere has been studied in the framework of the linear theory of ideal hydrodynamics. It has been shown that the initial equations under certain conditions can be reduced to the Klein-Gordon equation with constant coefficients. Its solutions describe traveling waves with a variable amplitude and wavenumber that are not reflected in the atmosphere despite its strong inhomogeneity. The wave energy flux at such reflectionless profiles holds, providing the possibility of the energy transfer to high altitudes. It has been shown that the Standard Earth Atmosphere is approximated well by four reflectionless profiles with small jumps in the gradient of the speed of sound. It is found that the Earth’s atmosphere is almost transparent in a wide frequency range; this feature explains the observation data and conclusions made on the basis of numerical solutions in the framework of the initial equations.