FLOW PAST A CIRCULAR-CYLINDER ON A BETA-PLANE

This paper gives analytical and numerical solutions for both westward and eastward flows past obstacles on a beta-plane. The flows are consi dered in the quasi-geostrophic limit where nonlinearity and viscosity allow deviations from purely geostrophic flow. Asymptotic solutions fo r the layer structure in almost-inviscid flow are given for westward f low past both circular and more elongated cylindrical obstacles. Struc tures are given for all strengths of nonlinearity from purely linear f low through to strongly nonlinear flows where viscosity is negligible and potential vorticity conserved. These structures are supported by a ccurate numerical computations. Results on detraining nonlinear wester n boundary layers and corner regions in Page & Johnson (1991) are used to present the full structure for eastward flow past an obstacle with a bluff rear face, completing previous analysis in Page & Johnson (19 90) of eastward flow past obstacles without rear stagnation points. Vi scous separation is discussed and analytical structures proposed for s eparated flows. These lead to predictions for the size of separated re gions that reproduce the behaviour observed in experiments and numeric al computations on beta-plane flows.