Seasonal Variation of the Taiwan Warm Current Water and Its underlying Mechanism

Based on the historical observed data and the modeling results, this paper investigated the seasonal variation of the Taiwan Warm Current Water (TWCW) using a cluster analysis method and examined the contributions of the Kuroshio onshore intrusion and the Taiwan Strait Warm Current (TSWC) to the TWCW on seasonal scales. As a result, most of the detailed phenomena associated with TWCW were revealed. The TWCW has obviously seasonal variation in its horizontal distribution, T-S characteristics and volume. And it consists of only the TWCSW from October to next March, but of both the TWCSW and the TWCDW from April to September. The volume of TWCW is maximum (13746 km³) in winter and minimum (11397 km³) in autumn. Being strongest (1.67 Sv) in July and weakest (0.2 Sv) in winter, the contributions of the TSWC to the TWCW are greatest in summer but smallest in winter. The results show that the Kuroshio onshore intrusion northeast of Taiwan is strongest in winter and weakest in summer. Hence, its contributions to the TWCW are greatest in winter and smallest in summer. By comparison, the Kuroshio onshore intrusion makes greater contributions to the TWCSW than the TSWC in the most months of a year except in summer months, the subsurface water from Kuroshio dominate the bottom layer of the TWCW. The analyzed results show that the local monsoon winds dominate the seasonality of the TWCW via Ekman dynamics, while the surface heat flux (which is clearly related to the change of the density field), can play a relative weaker role in the seasonality of the TWCW.