Volume transport in the East Taiwan Channel in response to different tracks of typhoons as revealed by HYCOM data

Northward inflow through the East Taiwan Channel is vital in modulation of water exchange processes off northeastern Taiwan, China. In addition to the effects of the Kuroshio Current and westward-propagating oceanic mesoscale eddies, the seas off eastern Taiwan, China, are frequently influenced by typhoons. Focusing on extrema of East Taiwan Channel volume transport (ETCVT) that appear within days of typhoon influence, this study investigated 124 historical cyclones including 91 typhoons that passed over the study sea area off eastern Taiwan, China. Based on 25-year HYbrid Coordinate Ocean Model (HYCOM) data, 71% of short-term (within 10 d) ETCVT absolute values with >5 Sv occurred under the influence of typhoons crossing the study sea area, and the maximum short-term ETCVT extrema induced by typhoons were 12.5 and -10.9 Sv. The ETCVT extrema induced by typhoons showed reasonable positive correlation with typhoon wind speed. More importantly, the ETCVT extrema differed in response to different typhoon tracks. Three types of typhoon were identified based on their track and impact on ETCVT. Representative typhoon cases were examined to elucidate the specifics of each typical response. Based on historical best track data and HYCOM data, it was established that Type I typhoons caused the ETCVT to exhibit a negative extremum followed by a positive extremum. All Type I, II, and III typhoons tended to result in typical ETCVT fluctuations in the surface mixing layer above the depth of 50–100 m, while Type II typhoons were more likely to induce ETCVT fluctuations in the subsurface layer. The findings of this study enhance understanding of ETCVT extrema that occur following typhoon passage, which is valuable for short-term physical-biogeochemical studies both in the study region and in areas downstream owing to the large net volume transport changes induced by typhoons.