EVIDENCE FOR A SATURATED SPECTRUM OF ATMOSPHERIC GRAVITY WAVES.

Abstract

The slope and power spectral density of atmospheric velocity fluctuations versus vertical wavenumber at large wavenumbers are observed to be nearly independent of altitude. We suggest that such a universality is due to saturation of short vertical-scale fluctuations. A brief review of linear gravity wave saturation theory indicates a physical basis for such spectra. It is demonstrated that observed saturation spectra are not solely due to individually saturated waves but most likely result from amplitude limiting instabilities arising from wave superposition. We also show that, while the spectrum is saturated at large wavenumbers, the total kinetic energy per unit mass and the characteristic vertical wavelength increase with altitude. Both of these predictions are consistent with observations.