A numerical study on the successive formation of Meddy-like lenses

[ 1] We present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom. With a cape along the coastline, water parcels in the bottom density current are shed into the offshore region, leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices. The cyclonic partner is more prominent at the surface, and the coupled vortices are carried by the mean current established in the offshore region. Parameter dependence of dipole generation is examined, which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat [Nof and Pichevin, 1996]. It is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface. A detailed analysis is given by a five-layer model forced by a water mass source/sink, which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z-coordinate model. We find that the dipole generation is due to the finite amplitude divergence/convergence of the baroclinic current passing the cape [ Stern and Chassignet, 2000]. The overall analyses suggest three necessary conditions for successive eddy formation: ( 1) a localized variation in the coastline causing the finite amplitude disturbance, ( 2) mixing of Mediterranean Water with the surrounding fluids leading to anticyclonic rotation of Meddies as well as cyclogenesis at the surface, and ( 3) background currents that advect the detached vortices out of the source region.