MULTIPLE ZONAL JETS IN A QUASI-GEOSTROPHIC MODEL OF THE ANTARCTIC CIRCUMPOLAR CURRENT

The presence of multiple zonal fronts in the Antarctic Circumpolar Cur rent (ACC), a phenomenon described as zonation, has been confirmed by many observations suggesting that the fronts are circumpolar in extent . In the context of quasigeostrophic turbulence models, Panetta has sh own that fronts associated with long-lived zonal jets develop spontane ously in very wide baroclinically unstable regions (of width large com pared with the Rossby radius of deformation). The present paper examin es the relevance of this mechanism to the zonation of the ACC, using a quasigeostrophic wind-forced channel model. Multiple jets appear when the forcing scale is wide enough, and they have horizontal scales and a strength that compares well with observations. However, in the pres ence of large-scale random topography, a different dynamical regime em erges in which the flow structure depends on the topographically contr olled stationary eddies.