Dissipation Dependence of the Jet Latitude

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Abstract
Zonally averaged flows in general circulation models exhibit strong sensitivity to the strength of the surface friction, subgrid-scale diffusion, and gravity wave drag. A commonly observed effect is that the midlatitude jets shift poleward as the drag on the zonal wind is decreased. In the present two-level primitive equation model the jet moves poleward with decreasing surface friction and with increasing subgrid-scale diffusion. The barotropic component of the jet shows much greater sensitivity than does the baroclinic component. Experiments using different values of friction for the eddies and for the zonal means reveal that the jet latitude is primarily controlled by the drag on the zonal means. The shift in the latitude of the jet is derived from the altered equilibrium response of the zonal wind to forcing by eddies when the friction is changed and the change in meridional structure of the eddy momentum fluxes in response to the modified zonal wind. The latter effect is also displayed by linear baroclinic modes.

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