Characterizing Residual Current Circulation and Its Response Mechanism to Wind at a Seasonal Scale Based on High-Frequency Radar Data

Residual current characteristics are indicators for the net transports of sediments, nutrients, and pollutants, and for the dilution and diffusion of soluble substances in coastal areas, yet their driving mechanisms remain poorly understood. Here, we studied the characteristics of surface residual currents along the west coast of the island of Ireland, as well as the response mechanisms to wind at a seasonal scale based on the continuous observation data of high-frequency radar (HFR) for one year. Our analyses indicate that wind has a significant effect on generating surface residual currents, with correlation coefficients of 0.6-0.8 between wind speeds and residual current speeds at both annual and seasonal scales. However, the correlation between the directions of residual currents and the wind was not as significant as speed, likely because the directions of residual currents were not only affected by sea surface wind, but also by land boundary conditions in the research area. Moreover, the residual currents had a significant eastward flow trend identical to the wind direction at the maximum wind speed time, during which the effect of the tide on residual currents was relatively weak. Additionally, when compared with wind fields, HFR surface flow fields and surface residual current fields show that wind is the dominant driver of the variations of surface and residual flow fields. These findings shed light on coastal ecological and environmental management and can assist in the prevention and mitigation of marine disasters, by providing helpful information for improving the ability and accuracy of forecasting coastal currents.