Laboratory studies of the effects of interrupted, sloping topography on intermediate depth boundary currents in linearly stratified fluids

Laboratory experiments are described which provide insight into the interac tion of intermediate depth boundary currents (IDBCs) with interrupted slopi ng topography. Specifically, they contribute to the debate over meddy forma tion on the Iberian continental slope. The experiments were per formed in a rectilinear rotating tank filled initially with a linearly-stratified flui d. A false bottom sloped away from the side-wall along which the current fl owed, and was interrupted by a gap of variable length. The effects of varyi ng gap length and rotation rate on the boundary current were observed. In the first of two sets of experiments, the current flowed above the slope , along the: vertical side wall. In the second, the current flowed along th e sloping bottom. In the former, current nose speed was consistent with geo strophic predictions, but decreased in the presence of a gap in the topogra phy. Kelvin wave radiation is postulated as a reason for this. The IDBCs ex hibited vortical lateral intrusions at values of the Burger number Bu = (N- 0/Omega)(2) at which counterpart flat-bottom studies had been stable, imply ing that the sloping topography had a de-stabilising effect. Energy measure ments and qualitative observations suggest the intrusions were due to mixed barotropic/baroclinic instabilities, the latter dominating at higher rotat ion rates. In the second configuration, four distinct hows were observed, distinguishe d by the deformation radius:gap width ratio R-D/G*. For a range of values o f R-D/G*, attached eddies formed at the upstream end of the gap. They remai ned at this position, unlike those in similar studies of surface boundary c urrents (Klinger. 1993). Their persistence and ability to move downstream-s alient factors for meddy - formation were greater for a finite gap size tha n a permanent change from sloping to flat bottom. (C) 2001 Elsevier Science B.V. All rights reserved.