Abstract: Based on sea surface current data observed by high-frequency ground-wave radar and ERA5 reanalysis wind data, this study investigates the daily variability of sea surface currents in the eastern coastal waters of Hainan Island using Empirical Orthogonal Function (EOF) analysis and Self-Organizing Map (SOM) classification. The results show that the major current variations can be represented by the first two EOF modes. The first mode reflects the strengthening and weakening of the alongshore background flow and represents the primary response of the regional current field to background wind forcing. The second mode mainly appears as a localized rotational anomaly, indicating adjustments in the local organization of the flow field. SOM further identifies four typical current patterns with clear differences in spatial structure, occurrence period, and current intensity. The sea surface current field in the study area exhibits pronounced seasonal and categorical characteristics, and its evolution is closely related to seasonal adjustments of the monsoonal background. This study supplements the understanding of the spatiotemporal variability of sea surface currents in the study area from the perspectives of dominant variability extraction and typical pattern identification.

Key words: high-frequency radar, coastal current characteristics, empirical orthogonal function (EOF), self-organizing map (SOM), monsoon