Features of Slope Intrusion Mesoscale Eddies in the Northern South China Sea

Some mesoscale eddies intrude over the continental slope in the northern South China Sea, supporting cross-shelf matter transport. We investigated the characteristics, the intruding tracks and formation mechanisms, of slope intrusion mesoscale eddies using satellite altimeter data and model outputs. In total, 36 and 22 slope intrusion anticyclonic and cyclonic eddies (SAEs/SCEs) are found, respectively. Slope intrusion eddies have longer lifetimes (similar to 58 days), smaller size (similar to 110 km), and greater eddy kinetic energy and vorticity compared to ordinary eddies but are more unstable and more easily deformed during their life cycles. The statistical results show that more slope intrusion eddies are generated during winter than other seasons. It is found that slope intrusion eddies mainly propagate westward/northwestward, and southwestward along the continental slope and shelf. Eddy intrusions occur mainly near the Dongsha Islands, east of Hainan, and north of the Xisha Islands. SAEs continue to propagate onshore after arrival at the continental slope, while SCEs dissipate more quickly. Using mooring data, we found that eddy-ambient flow interaction could cause the differences between SAEs and SCEs around the Dongsha Islands. Energy conversion was analyzed in these three regions using numerical products. During intrusion, eddies lose eddy kinetic energy and ambient flows gain energy.