The characteristics of the recirculating bulge region in coastal buoyant outflows
A relatively large recirculating gyre, or bulge (anticyclonic buoyant lens) region attached to the source has been observed to occur in some numerical simulations and in some oceanic outflows. The purpose of this paper is to determine the dynamics of such recirculating bulge regions. Laboratory experiments were conducted for the purpose of examining the characteristics, evolution, and impact of a recirculating bulge in a coastal buoyant outflow. All experiments were performed such that the buoyant layer was thin compared to the total water depth, and the width of the bay exit was approximately equal to the internal Rossby deformation radius of the buoyant outflow. The geometry of the bay-exit (radius of curvature and exit angle) was varied in order to produce experiments with recirculating bulge formation, and experiments without. Measurements of the density and velocity fields were undertaken. The dimensions of the recirculating bulge were found to evolve identically (when appropriately scaled) for all experiments in which such a bulge formed, regardless of bay-exit geometry. When recirculating bulges formed, it was determined that the freshwater storage within the bulge was approximately 60 -70% of the source freshwater flux. The impact on the attached coastal current downshelf of the recirculating bulge was found to be significant: the width, length, and velocities of such attached coastal currents were much reduced in comparison to coastal currents that evolved in the absence of a recirculating bulge. Growth rates of the bulge were measured with time: the recirculating bulge was found to grow radially as ~t2/5 and vertically as ~t1/5. Baroclinic instabilities were observed in the recirculating bulge. The instabilities evolved as multiple rotating cores within the larger anticyclonic gyre. The presence of the instabilities in the recirculating bulge may account for its relatively large radial growth but weak vertical growth.
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Document Type: Research Article
Publication date: July 1, 2003
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