Seasonal variation of the Taiwan Warm Current Water and its underlying mechanism

Abstract

Based on the historical observed data and the modeling results, this paper investigated the seasonal variations in 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 time scales. The TWCW has obviously seasonal variation in its horizontal distribution, T-S characteristics and volume. The volume of TWCW is maximum (13 746 km3) in winter and minimum (11 397 km3) in autumn. As to the contributions to the TWCW, the TSWC is greatest in summer and smallest in winter, while the Kuroshio onshore intrusion northeast of Taiwan Island is strongest in winter and weakest in summer. By comparison, the Kuroshio onshore intrusion make greater contributions to the Taiwan Warm Current Surface Water (TWCSW) than the TSWC for most of the year, except for in the summertime (from June to August), while the Kuroshio Subsurface Water (KSSW) dominate the Taiwan Warm Current Deep Water (TWCDW). The analysis results demonstrate that the local monsoon winds is the dominant factor controlling the seasonal variation in the TWCW volume via Ekman dynamics, while the surface heat flux can play a secondary role via the joint effect of baroclinicity and relief.