Interactions of mesoscale eddy and western boundary current: A reduced-gravity numerical model study

A reduced-gravity primitive equation eddy resolving model is used to study the interaction of a typhoon-induced eddy and a wind-driven general circulation. A typhoon-induced eddy is characterized by a core with a relative vorticity of the same order as the local Coriolis parameter. This eddy is neutrally stable relative to a disturbance induced by the westward advection of the eddy, due to the planetary beta-effect. Hence, its evolution in the open ocean is similar to the classical frontal geostrophic eddy. Within the western boundary flow regime, the eddy is entrained northward by the mean circulation. This northward eddy advection and the mean-vorticity advection due to eddy flow induce another disturbance with a north-south asymmetry into the circular eddy. Together with the zonal asymmetric disturbance, associated with the planetary beta-effect, the original circular eddy becomes unstable. The nonlinear eddy-flow interactions in the eastern flank of a western boundary current causes the eddy to deform quickly into an ellipse and lose its waters and energy into the mean circulation.