Submesoscale Eddies Observation Using High-Frequency Radars: A Case Study in the Northern South China Sea

Eddies are of great concern to ship operations and have an important influence on heat transfer in the sea. In this article, a highly concurrent and accurate method incorporating the winding angles and density-based clustering (WA-DBC) algorithms is proposed for automatic eddy detection from surface current maps generated by high-frequency radars (HFRs). As a case study, eddies and their characteristics, such as centers, radii, and lifespans, were extracted using both the WA-DBC and vector geometry algorithms from the HFR surface current maps of the north of Qiongzhou Strait, South China Sea. The eddy trajectories obtained show that most eddies in this region during the experiment period had a radius of 3–30 km and negative correlation existed between the radius and the life span (i.e., eddies with a smaller radius survived a longer lifespan). Furthermore, most of the eddies appeared in the central part of the study area and lasted for 40–100 min. This study shows that HFR is useful for detecting submesocale eddies for research works and applications in marine observation.