| description abstract | ddies off the Strait of Luzon (termed here as ?Leddies,? analogous to ?Teddies? originating from the Indonesian Throughflow) are formed rapidly and migrate swiftly. Their migration rate (~10?20 cm s?1) is an order of magnitude faster than that of most eddies of the same scale (~1 cm s?1). On the basis of observations, it has been suggested earlier that the rapid generation process is due to the southeast monsoon.Here, the authors place this earlier suggestion on a more solid ground by developing both analytical and process-oriented numerical models. Because the eddies are formed by the injection of foreign, lighter Kuroshio water into the South China Sea (SCS), the eddies are modeled as lenses: that is, ?bullets? that completely encapsulate the mass anomaly associated with them. It turns out that the rings migrate at an angle α (between 0° and 90°) to the right of the wind direction {i.e., tan?1[(2 ? ?)f2R/8g?CD, where in conventional notation ? is the vorticity, R the eddy radius, and CD the interfacial friction coefficient along the lower interface of the lens}. Their fast migration speed is given by 2(τS/?W)(sinα)/fH, where τS is the wind stress on the surface, ?w the water density, and H is the maximum eddy depth. With high interfacial drag (i.e., large CD), the rings move relatively slowly (but still a lot faster than Rossby waves) in the wind direction, whereas with low drag they move fast at 90° to the right. These analytically predicted values are in good agreement with isopycnic numerical simulations. | |
