Stability of Four-Gyre Flow Pattern in a Barotropic Model on a Rotating Hemisphere

Abstract

The stability of barotropic flows on a rotating hemisphere with the rigid boundary along the meridional lines, is studied under several wind-forcings, which bring about four-gyre flow patterns. This flow may be a correspondent on a rotating sphere to the two-gyre flow on the β-plane, which has been studied so far as a model of the westward intensification. As the wind-forcing is increased, an oscillating instability arises from the steady flow solution of westward intensification, without a preceding pitchfork bifurcation often observed in the β-plane. The critical magnitude of the forcing wind is not a monotonic function of the size of the middle gyres.