A numerical study on the response of wave number spectra of atmospheric gravity waves to lower atmospheric forcing

Abstract

Starting from a set of nonrotating, fully nonlinear basic atmospheric kinetic equations, we numerically study the response of wave number spectra for atmospheric gravity wavefields to different excitation sources. The simulation results show that only when excited by a localized random momentum source do the horizontal and vertical wave number spectra of the gravity wavefields exhibit a “quasi‐universal” spectral structure, indicating that the random characteristic of the source may play an important role in forming a “universal” spectrum. By adjusting several tunable parameters in our model, we numerically study the influences of the source properties and background winds on the wave number spectra. Our simulations suggest that the intermittency and asymmetry of wave sources and a sheared background wind will lead to shallower wave number spectra. Apart from these differences, vertical wave number spectra arising from different sources and background conditions exhibit some conformities. For instance, generally, the spectral slopes for the vertical wind fluctuations are larger (in magnitude) than those for the horizontal wind and temperature fluctuations, and the slopes for the horizontal wind fluctuations are usually slightly smaller than those for the temperature fluctuations.