Quasigeostropic models of mid-latitude gyres are driven by an Ekman pumping term that is proportional to the wind stress curl. Since the wind stress is considered to be arbitrarily specifiable, the Ekman pumping term does not generally integrate to zero and mass is not balanced (to leading order) for timescales long compard to the Coriolis timescale. In particular, the strong vertical velocities that occur where a wind stress is applied tangent to horizontal boundaries are not accounted for, except implicitly--by a 2-dimensionally divergent viscous boundary layer. Here, we suggest that this wall layer interacts with the adjacent QG flow in the high Reynolds number limit. It is argued that this causes QG to give way to semi-geostrophy near the wall and that the `coastal upwelling' associated with a wind stress applied at vertical walls should be explicitly accounted for in modeling mid-latitude gyres. Analaogus problems with the shallow water version of this problem are also discussed, as are implications to the problem of inertial runaway in simple gyre models.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics