A numerical study of infrasound scattering from atmospheric inhomogeneities based on the 3-D unsteady compressible Navier-Stokes equations

Abstract

A direct numerical simulation of the compressible unsteady Navier-Stokes equations is performed to investigate the 3-D nonlinear acoustic field generated by a high-amplitude infrasonic source placed at ground level in a realistic atmosphere. High-order finite differences and a Runge-Kutta time integration scheme originally developed for aeroacoustic applications are employed. The atmosphere is parametrized as a stationary and vertically stratified medium, constructed by specifying a speed of sound and a mean wind profiles which mimic the main trends observed during the Misty-Picture experiment. In the present talk, after a general description of the acoustic field observed up to 140 km altitude and 450 km range, the scattering from stratospheric inhomogeneities is investigated. The spectrum of the scattered wave recorded at ground level is more particularly discussed and its dependence on the spectral properties of the inhomogeneities is highlighted. A fast method for computing the scattered field, based on a wavelet representation of the temperature and wind fluctuations, is finally presented.