Identification and Analysis of Mesoscale Eddies in the South China Sea

Mesoscale eddy is an important phenomenon in the ocean. The detection of mesoscale eddy is of great significance to the study of marine ecological environment, dynamics, climate and other fields. Based on the daily satellite altimeter data from Jan 1, 2014 to Dec 31, 2018, this study used the SLA closed contour method to identify mesoscale eddies in the South China Sea (SCS). Then, the SCS was divided into 4 regions to count and analyze the spatiotemporal changes of the quantity, radius and amplitude of the mesoscale eddies in the SCS. The results show that the mesoscale eddies in the SCS are mainly distributed in the northeast to southwest region with water depth greater than 200 m, among which the western sea of Luzon Strait and the eastern sea of south-central Vietnam are the most active areas of the eddies. The number of cyclonic eddies is slightly more than that of anticyclonic eddies, with an average of 21 cyclonic eddies and 19 anticyclonic eddies per day. The radii of these eddies are mainly distributed between 30 and 110 km, eddies with a radius of more than 200 km are very few, and their amplitudes are mainly distributed between 1 and 3 cm. In general, the anticyclonic eddies have a larger radius and amplitude than the cyclonic eddies. The mesoscale eddies in the SCS generally have obvious seasonal changes. Winter is beneficial to the generation of cyclonic eddies and summer is beneficial to the generation of anticyclonic eddies. Furthermore, the eddies change under various influence mechanisms such as monsoon, Kuroshio current, seabed topography, and barotropic instability were discussed. Meanwhile, the seasonal evolution of the average eddy kinetic energy of the SCS was also studied. The results show that the monsoon is the main driving mechanism for the generation of mesoscale eddies in the SCS, and the Kuroshio has a significant impact on the eddies in the west side of the Luzon Strait. The eddy kinetic energy of the SCS presents distinct forms with seasonal changes, and the western seas of the Luzon Strait and the seas east of south-central Vietnam are the areas with high values of eddy kinetic energy.