Observations in the context of numerical modeling examine the dynamics underlying eddy-Kuroshio interactions


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Mesoscale eddies are everywhere in the ocean. These ocean swirls of either clockwise or counterclockwise spinning with diameter of about 100-300 km and rounding current speed of about 0.5 m/s, carrying energy and certain type of water mass, move westward and eventually reach the western boundary of each ocean. The evolution of these eddies and the interaction which occurs

when they encounter the western boundary current, e.g. the Kuroshio in the western North Pacific, is important in redistributing ocean energy and, in turn, shaping the large scale ocean circulation. This study focuses on the processes underlying the interaction of nonlinear mesoscale eddies with the Kuroshio, which have not yet been thoroughly investigated in the literature. Using pressure-sensor equipped echo sounder and satellite observations interpreted in the context of semi-idealized numerical simulations (Fig. 1), this study find (1) locally, eddy arrivals modify velocity structure in the Kuroshio first, followed by changes in sea level and isopycnal depths leading to seesaw-like variations of the sea level and density slopes across the Kuroshio, and (2) modeled remote effects, i.e., Kuroshio intrusions, manifest in the Luzon Strait and on the East China Sea shelf and depend on the eddies’ impingement latitude, strength, and polarity (Fig. 2).

Fig. 1 Numerical simulations for (a) a cyclonic eddy impinging and (b) an anticyclonic eddy impinging on the Kuroshio.

Fig. 2 Schematic showing Local (left panels) and remote effects (right panels) occur when eddies of both signs impinging on the Kuroshio.