A Study on Taiwan Island-Trapped Circulation

Due to the restriction of near-shore observation in satellite altimeter data, and the measured data could only provide fragment of the whole near-shore flow. So the research on near-shore flow around Taiwan (where in the east of China and beside Kuroshio) is less than the mesoscale circulation like Kuroshio. Previous studies showed that coastal-trapped wave could exist in island and even generated a circle circulation around island. Because of the different geographical environment and the scale of the island, whether there is island-trapped circulation around Taiwan and its physical mechanism is what this study wants to explore. By using velocity gridded data from buoy drifters, we found there is clockwise circulation around Taiwan western and northeastern in summer and completely opposite in winter. Furthermore, the trajectory of the buoy which drifted clockwise around Taiwan were concentrated and near the shore. In contrast, the trajectory which in anticlockwise direction almost round a circle around Taiwan but far away from the shore. To investigate this mechanism, we used satellite wind data and found that the monsoon may cause this result with Ekman transport. In HYCOM data, the EOF result also showed that island-trapped circulation has seasonal change in mode 2 result. Now we are using the MCC method with Himawari-8 high resolution data to calculate the near-shore flow, and using the linear coastal-trapped wave model to analyze these data. Hope to find the physical mechanism of this island-trapped circulation.