GYRE FORMATION AT A CORNER BY ROTATING BAROTROPIC COASTAL FLOWS ALONGA SLOPE

A series of laboratory experiments explored the behavior of a barotrop ic coastal current that encounters a convex corner. In a tank rotating in the counter-clockwise sense, the current was pumped along bottom t opography which sloped upwards to a coast on the right of the current (looking downstream). Downstream of the current source, the isobaths e xecuted a 90 degrees turn to the right. The coastal current quickly at tained a steady state in which, for Rossby numbers greater than about 0.1, it separated from the shore at the corner, flowed around the peri meter of an anticyclonic gyre, and reattached to the coast further dow nstream. The normalized width of the gyre was proportional to the Ross by number of the current upstream of the corner, and the gyre width in creased when the relative change in depth across the current decreased . Both these effects are due to the weakening of the rotation-induced constraint that the flow should follow isobaths. When the Ekman number was varied by a factor of approximately four there were no systematic variations in the gyre width. The sharpness of the corner also did no t affect gyre width, except when the inertial radius, which is the cur rent speed divided by the Coriolis parameter, was less than or equal t o the corner radius of curvature. In that case, the current separation was not accompanied by the presence of a gyre. The surface velocity f ield was found to be nondivergent even in regions where the current wa s flowing into deeper or shallower water; this result implies strong v ertical shears in the horizontal velocity. Though the nondivergence of the surface flow field implied that complete separation from the bott om was possible, no such separation was seen in qualitative observatio ns of a vertical section of flow.