The horizontal kinetic energy spectrum and spectral budget simulated by a high-resolution troposphere-stratosphere-mesosphere GCM

Horizontal kinetic energy spectra simulated by high-resolution versions of the Geophysical Fluid Dynamics Laboratory SKYHI middle-atmosphere general c irculation model are examined. The model versions considered resolve height s between the ground and similar to 80 km, and the horizontal grid spacing of the highest-resolution version is about 35 km. Tropospheric kinetic ener gy spectra show the familiar similar to -3 power-law dependence on horizont al wavenumber for wavelengths between about 5000 and 500 km and have a slop e of similar to -5/ 3 at smaller wavelengths. Qualitatively similar behavio r is seen in the stratosphere and mesosphere, but the wavelength marking th e transition to the shallow regime increases with height, taking a value of similar to 2000 km in the stratosphere and similar to 4000 km in the mesos phere. The global spectral kinetic energy budget for various height ranges is comp uted as a function of total horizontal wavenumber. Contributions to the kin etic energy tendency from nonlinear advective processes, from conversion of available potential energy, from mechanical fluxes through the horizontal boundaries of the region, and from parameterized subgrid-scale dissipation are all examined. In the troposphere, advective contributions are negative at large scales and positive over the rest of the spectrum. This is consist ent with a predominantly downscale nonlinear cascade of kinetic energy into the mesoscale. The global kinetic energy budget in the middle atmosphere d iffers significantly from that in the troposphere, with the positive contri butions at most scales coming predominantly from vertical energy fluxes. The kinetic energy spectra calculated from two model versions with differen t horizontal resolution are compared. Differences between the spectra over the resolved range of the lower-resolution version are smallest in the trop osphere and increase with height, owing mainly to large differences in the divergent components. The result suggests that the parameterization of dyna mical subgrid-scale processes in middle-atmosphere general circulation mode ls, as well as in high-resolution tropospheric general circulation models, may need to be critically reevaluated.