Decaying 2d turbulence in basin and meridional channel settings

Classic theories of westward intensification appeal to both the β-effect and to dissipation. It is less clear why geostrophic flow should be westward-intensified in the high Reynolds number, long time limit. Decaying 2d turbulence in a basin, for example, excites Fofonoff-like modes which have equally energetic eastern and western boundary layers. The Fofonoff modes, however, require a northern or southern wall to support an eastward current. Here, we compare decaying β-plane (2d) turbulence in basin and meridional channel settings. The latter removes the northern/southern walls so that a Fofonoff-like flow cannot result. Flows resulting from small-scale, random initial conditions are characterized as functions of the Rhines scale and resolution. The time-mean flow of the meridional channel favorizes the emergence of westward-intensified zonal jets. Particular attention is paid to the degree to which this is true for the late time flow and to the fraction of energy going into the linear basin modes.