Characterization of longshore currents in southern East China Sea during summer and autumn

Current characteristics and vertical variations during summer and autumn in the southern East China Sea were investigated by measuring current profile, tide, wind, and wave data for 90 d from July 28 to October 25, 2015. Our results are: (1) The current was mainly a (clockwise) rotating flow, displaying reciprocating flow characteristics, and vertically the current directions were the same throughout the vertical profile. (2) The horizontal current speed was strongest during August (summer) with an average speed of 51.8 cm/s. The average current speeds during spring tides were highest in August and weakest in September, with speeds of 59.9 and 42.8 cm/s, respectively. (3) Considerable differences exist in average current speeds in different layers and seasons. The highest average current speeds were found in the middle–upper layers in August and in the middle–lower layers in September and October. (4) The residual current speed was highest in August, when the speed was 12.5–47.1 cm/s, whereas the vertical average current speed was 34.3 cm/s. The depth-averaged residual current speeds in September and October were only 50% of that in August, and the residual current direction gradually rotated in a counter-clockwise direction from the lower to surface layers. (5) Typhoon waves had a significant influence on the currents, and even affected the middle and lower water layers at depths of >70.0 m. Our results showed that the currents are controlled by the dynamic interplay of the Taiwan Warm Current, incursion of the Kuroshio Current onto the continental shelf, and monsoonal changes.