Temporal and spatial variability of volume transport of the Kuroshio in the East China Sea

Abstract

The temporal and spatial variability of absolute geostrophic volume transport of the Kuroshio is examined using hydrographic and surface current data collected by the Japan Meteorological Agency on 39 transport sections made at six transects in the Fast China Sea and one transect just outside the East China Sea during the three-year period 1986–1988. The Kuroshio volume transport ( KVT) is estimated by integration over each transect of the downstream (positive) part of the geostrophic velocity referenced to the observed surface current. Our analysis indicates that, on average, only about 25% of the KVT inside the East China Sea is due to the baroclinic or vertically varying component. While KVT exhibits a small-scale temporal and spatial variability with downstream phase speeds of order 8–19 km day −1 and wavelengths of order 150–375 km, mean KVT is spatially uniform within the East China Sea. KVT has significant annual and interannual variations: KVT is large in summer, is positively correlated with local downstream wind stress, and is large during large meander events of the Kuroshio south of Japan. Our best estimate of the mean KVT in the East China Sea during 1986–1988 is 23.7 Sv ± 2.0 Sv. This represents about one-half of the mean interior Sverdrup transport at this latitude. The Kuroshio quickly absorbs most of the remaining interior Sverdrup transport after it exits the East China Sea through the Tokara Strait.