Erosion of a Surface Vortex by a Seamount.
Résumé
Numerical experiments are carried out on the f plane, using a shallow-water isopycnal model, to analyze the behavior of a surface-intensified anticyclonic vortex when it encounters an isolated seamount. The advection by the vortex of deep fluid parcels across the isobaths is known to generate deep anticyclonic and cyclonic circulations above and near the bathymetry, respectively. These circulations are shown to exert a strong shear on the upper layers, which causes an erosion of the initial vortex by filamentation. The erosion often results in a subdivision of the eddy. While the eroded original structure forms a dipole with the deep cyclone and is advected away, the filaments torn off from the original core aggregate into a new eddy above the seamount. Splitting in more than two structures is sometimes observed. The erosion process is quantified by the bulk volume integral of the eddy potential vorticity anomaly. A sensitivity study to different parameters of the configuration (distance between vortex and seamount, vortex radius, seamount radius, seamount height, or stratification) shows that the intensities of the deep anticyclonic and cyclonic circulations and the vortex erosion are governed both by the reservoir of positive potential vorticity associated with the seamount and by the strength of the cross-isobath flow induced by the eddy.