The geometry of mesoscale eddies in the South China Sea: characteristics and implications

The symmetrical circular shape of mesoscale eddies has been widely used in their scientific researches.Recently,an elliptical average eddy shape has been confirmed for eddies in the global ocean using multi-satellite altimeter data.As a regional extension of a previous study on the geometry of global eddies,a mean eddy shape in the South China Sea(SCS)has been derived by averaging a large number of orientational eddy boundaries.The mean shape is approximately a mathematic ellipse with a semimajor axis of 101.3 km and a semiminor axis of 61.3 km.Its size is larger than the global one.The principal eddy orientation in the SCS is 74°/254°(nearly northeast-southwest),different from that of eddies in the global ocean(171°/351°,nearly east–west).Composite analyses of chlorophyll(CHL)concentrations and sea surface temperature anomalies(SSTA)indicate a dipole structure for circular eddies in the non-rotated coordinate system.While a monopole structure for elliptical eddies in the eddy-centric coordinate system is obtained.The results demonstrate that the elliptical shape of eddies affects oceanographical variables.The findings provide a new approach for exploring the role of air–sea interactions on oceanic eddies.