Published online by Cambridge University Press: 11 April 2006
We consider the flow of rapidly rotating fluid over topography in a circular basin. The equations of motion (here the inviscid quasi-geostrophic vorticity equations) can be integrated exactly for certain zonally averaged currents. The assumption of the existence of a specified zonal current is equivalent to the assumption of no upstream influence in the unbounded case. It is unlikely that such solutions can be realized in experiments with real fluids for the presence of viscosity, however small, causes ‘zonal influence’ independent of the magnitude of the viscosity at times larger than the spin-up time. For times smaller than the spin-up time decaying transients can cause zonal influence which increases in magnitude with decreasing viscosity.