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Abstract

Data from several middle-atmosphere general circulation models are used to calculate kinetic energy spectra as a function of total horizontal wavenumber n. The horizontal and vertical resolution between models varies but all have upper. boundaries at heights • 80 km. Tropospheric spectra show power-law behavior with slopes slightly shallower than-3 for wavenumbers n • 10 (horizontal wavelengths • 4000 km) and are dominated by the rotational part of the flow. These spectra agree well with those calculated using data obtained from a global assimilation model and with the results of previous observational studies. Stratospheric spectra have larger amplitudes than tropospheric ones at planetary scales and smaller amplitudes at smaller scales. Mesospheric spectra are characterized by enhanced spectral amplitudes at all wavenumbers compared to the stratosphere and spectral slopes in the wavenumber range n • 10 are generally shallower. Stratospheric and mesospheric spectra include approximately equal contributions from the rotational and divergent parts of the flow for n • 20 in all models. These features appear to be independent of model resolution. The divergent part of the flow, presumably associated with explicitly resolved inertiogravity waves in the models, increases more rapidly with height above the lower stratosphere than the rotational part. The divergent part is fairly insensitive to season, whereas the rotational part changes considerably between January and July in the middle-atmosphere region. Spectral amplitudes and vertical growth rates of both parts vary widely between models for a given season. The horizontal diffusion schemes used by the models are compared in an attempt to explain some of these differences. Nellsen, 1978; Koshyk and Boer, 1995; Nastrom et al., 1984]. On scales between about 4000 and 400 km, the spectra show slopes of •0-3, are dominated by the rotational part of the flow, and are associated with downscale enstrophy fluxes [Boer and Shepherd, 1983], all