On the Genesis of the South China Sea Mesoscale Eddies

Abstract

The climatology of the mesoscale eddies in the upper layer of the South China Sea (SCS) is investigated for an understanding of its genesis using the outputs from a 1/12.5◦ ocean reanalysis. Employed is a recently developed multiscale energetics formalism on the basis of a multiscale window transform (MWT) and the theory of canonical transfer. Three scale windows, namely, background flow, mesoscale eddy and synoptic eddy, are differentiated, and fields on different scales are reconstructed henceforth. Diagnosis of the mesoscale eddy energy budget reveals that barotropic and baroclinic instabilities, wind work, advection and pressure work are essential ingredients of the eddy energy sources and sinks in the SCS, but their contributions vary from region to region. In the southwestern part of the SCS, the regional mesoscale eddy energy is mainly generated by barotropic instability, while in the northeastern SCS, baroclinic instability and the wind working directly on the eddies are the two dominant eddy generation processes. The eddies southwest of Taiwan are damped by outward energy transport via advection, while the decay of those southeast of Vietnam is due to pressure work. The three-scale framework also reveals that the interaction between the mesoscale eddies and higher-frequency synoptic eddies mainly serves as a sink for the mesoscale eddy energy in the SCS, except for the northeastern SCS, where significant inverse cascade of kinetic energy is found.