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 parameter-ization 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 &ωcirc;. 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 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 α&ωcirc;[sup -0.6] &ωcirc;[sup -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.