On acoustic N-wave reflections from atmospheric layered inhomogeneities

The nonlinear propagation of acoustic pulses from a point source of an explosive character (surface explosion or volcano) throughout the atmosphere with stratified wind-velocity and temperature inhomogeneities is studied. The nonlinear distortions of acoustic pulse and its transformation into an N-wave during its propagation to the upper atmosphere are analyzed in the context of a modified Burgers’ equation which takes into account a geometric ray-tube divergence simultaneously with an increase in both nonlinear and dissipative effects with height due to a decrease in atmospheric density. The problem of reflection of a spherical N-wave from an atmospheric inhomogeneous layer with model vertical wind-velocity and temperature fluctuations having a vertical spectrum that is close to that observed within the middle atmosphere is considered. The relation between the parameters (form, length, frequency spectrum, and intensity) of signals reflected from an atmospheric inhomogeneous layer and the parameters of the atmospheric fine layered structure at reflection heights is analyzed. The theoretically predicted forms of signals reflected from stratified inhomogeneities within the stratosphere and the lower thermosphere are compared to the observed typical forms of both stratospheric and thermospheric arrivals from surface explosions and volcanoes in the zones of an acoustic shadow.