Interactions Between the Mesoscale Eddy Dipole and Eastward Jet in the Western South China Sea

Abstract

The mesoscale eddy dipole (MED) in the western South China Sea is characterized by a seasonal pair of cold and warm eddies, which typically appear off the Vietnam coast from July to September, accompanied by an eastward jet (EJ) traversing the MED between 11°N and 12°N. However, detailed investigations into the interactions between the MED and EJ remain limited in previous studies. In this study, the interactions between the MED and EJ in 2011 are examined from both morphologic and energetic perspectives using the Oceanic Regional Circulation and Tidal Model. Variations in their intensity and position are strongly correlated. Multiscale energy transfer analysis reveals a notable positive energy cascade from the EJ to the MED. Mixed barotropic and baroclinic instabilities, primarily occurring in the upstream region of the EJ, promote the formation and development of the MED. In contrast, in the mid‐downstream region, part of kinetic energy is inversely transferred from mesoscale eddies to the large‐scale circulation, facilitating the stretching and intensification of the EJ. The distribution of eddy–mean flow energy transfer is distinctly anisotropic, with stronger energetic interactions in the upstream part of the EJ horizontally and within the cold eddy of the MED meridionally. This study advances our understanding and underscores the need for greater attention to this highly seasonal eddy–mean flow dynamic system.