Latitudinal variations observed in gravity waves with short vertical wavelengths

Abstract

Knowledge of the latitudinal variations in the occurrence of gravity waves is important for their parameterization in global models. Observations of gravity waves with short vertical scales have shown a pronounced peak in wave activity at tropical latitudes. In this paper, it is shown that such a peak may be a natural consequence of the latitudinal variation in the Coriolis parameter, which controls the lower limit for gravity-wave intrinsic frequencies ̂w. Two distinct but related effects of this parameter on observations of gravity-wave activity are explained and explored with a simple model. The results are also compared to observed latitudinal variations in gravity-wave activity. The authors formally distinguish between observed gravity-wave spectra and what is called gravity-wave "source spectra," the latter being appropriate for input to gravity-wave parameterizations. The results suggest that the ̂w-5ß dependence of the gravity-wave energy spectrum commonly assumed as input to parameterizations is likely too steeply sloped. Much more shallowly sloped spectra for gravity-wave parameterization input σ̂w-0.6 - ̂w-0.7 show better agreement with observations. The results also underscore the potential importance of intermittency in gravity-wave sources to the interpretation of gravity-wave observations.