Study of ocean current at multiple time scales based on the high frequency surface wave radar

The coastal current presents complex changes in spatiotemporal scale due to various dynamic processes and shoreline islands. High frequency surface wave radar has become an effective method to solve these problems because of its wide coverage area and high temporal resolution. Several years ocean current data was collected in Zhoushan sea area, the dynamic processes of the ocean in tide cycle, extreme events, intermonth and interannual time scales in this area were interpreted by using tidal current harmonic analysis, low pass filtering and correlation analysis. The results depicted that the Zhoushan sea area is a regular semi-diurnal tide area, and the current movement is mainly in the form of rotating current. The distribution of current velocity in investigation area illustrated a decreasing trend from northeast to southwest. Interannual variation of residual current in the Zhoushan sea area is not significant, however the obvious intermonth variation characteristic of the residual current was detected. In winter, the flow is southward, and its larger near shore than outside sea. On the contrary, the flow velocity is stronger and the spatial distribution is more uniform in summer. The correlation between wind and residual current was analyzed, during strong winds, the correlation coefficient between wind speed and residual current velocity ranged from 0.48 to 0.90, and the correlation coefficient between wind direction and residual current direction ranged from 0.55 to 0.68. When extreme events occur, the correlation coefficients of velocity and direction are 0.92 and 0.91, respectively. By way of conclusion, the analysis of high frequency surface wave radar data can well reflect the temporal and spatial characteristics of ocean currents in Zhoushan sea area, which provide a basis for marine disaster monitoring, pollutants and algal bloom transport research.