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

Folkard, AM and Davies, PA (2001) Laboratory studies of the effects of interrupted, sloping topography on intermediate depth boundary currents in linearly stratified fluids. Dynamics of Atmospheres and Oceans, 33 (4). pp. 239-261. ISSN 0377-0265

Abstract

Laboratory experiments are described which provide insight into the interaction of intermediate depth boundary currents (IDBCs) with interrupted sloping topography. Specifically, they contribute to the debate over meddy formation on the Iberian continental slope. The experiments were performed in a rectilinear rotating tank filled initially with a linearly-stratified fluid. A false bottom sloped away from the side-wall along which the current flowed, and was interrupted by a gap of variable length. The effects of varying 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 sidewall. In the second, the current flowed along the sloping bottom. In the former, current nose speed was consistent with geostrophic predictions, but decreased in the presence of a gap in the topography. Kelvin wave radiation is postulated as a reason for this. The IDBCs exhibited vortical lateral intrusions at values of the Burger number Bu = (N0/Ω)2 at which counterpart flat-bottom studies had been stable, implying that the sloping topography had a de-stabilising effect. Energy measurements and qualitative observations suggest the intrusions were due to mixed barotropic/baroclinic instabilities, the latter dominating at higher rotation rates. In the second configuration, four distinct flows were observed, distinguished by the deformation radius:gap width ratio RD/G*. For a range of values of RD/G*, attached eddies formed at the upstream end of the gap. They remained at this position, unlike those in similar studies of surface boundary currents (Klinger, 1993). Their persistence and ability to move downstream � salient factors for meddy � formation were greater for a finite gap size than a permanent change from sloping to flat bottom.