Responses of the Kuroshio to Typhoons Observed by Moored Instruments off Taiwan

Evolving processes of pycnocline depth and volume transport variability across the Kuroshio during the influence of typhoons were observed using six pressure sensor-equipped inverted echo sounders (PIESs) and three acoustic Doppler current profilers (ADCPs) deployed east of Taiwan. During an approximately 2-year observation (November 2012 through October 2014), eight typhoons passed across or near the mooring array. The responses of the Kuroshio to the strongest two typhoons, Soulik and Usagi, were analyzed. Soulik was a Category 4 typhoon translated towards the west-northwest about 80 km north of the mooring array during July 11 and 12, 2013. The transport was 2 Sv (1 Sv=10⁶ m³ s^-1) decreased on July 12, and the acoustic travel time (pycnocline depth) was increased (depressed) subsequently on 7/13 during the period of typhoon influence. Usagi was a Category 5 typhoon and its track was ~400 km south of the array translated west-northwestward through the Luzon Strait from September 20 to 21, 2013. Unlike the influence of Soulik, Usagi caused acoustic travel time (pycnocline depth) decrease (heaving) first on September 21 and then volume transport increase (~2 Sv) on September 22. The spatial and temporal variation of typhoon wind stress and wind stress curl, and the strength and translation speed of typhoon lead to complicated influences from typhoons to the Kuroshio east of Taiwan.