How many waves are in the gravity wave spectrum?

Parametric modelling of density perturbation measurements obtained with the University of Western Ontario's Purple Crow Lidar on 5 nights are used to infer that the typical vertical wavenumber spectrum in the upper stratosphe re is dominated by a few quasi-monochromatic waves. In general only 2 of th ese waves, with growth or decay rates on the order of 1/(14 km) or less, ca rry most of the spectral energy. These waves are present about half the tim e on the nights studied. When analyzed using classical spectral techniques these waves appear to form a continuous spectrum. These results may help ex plain why general circulation models obtain reasonable climatologies when g ravity wave parameterization schemes based on a small number of propagating gravity waves are employed.