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To measure the Kuroshio and its recirculation south of Japan, a group called ASUKA (affiliated surveys of the Kuroshio off Cape Ashizuri) from Japan and the U.S. carried out observations along a line crossing the Kuroshio, which was chosen to coincide with a track of the altimetry satellite TOPEX/POSEIDON. In October 1993, we deployed nine moorings equipped with 33 current meters and two ADCPs (acoustic Doppler current profilers), and ten inverted echo sounders, which were maintained for two years until November 1995. During that period, we carried out repeated hydrographic sections (41 times) and towed-ADCP sections (12 times) to estimate upper layer velocities, which cannot be measured adequately by the present moored instruments. This effort was intended to be the WOCE PCM5 array and a fundamental study for GOOS (Global Ocean Observing System). From first-year moored current meter data and repeated hydrography data, we estimate geostrophic velocities normal to the observation line and referred to velocities observed at a nominal depth of 700 m. The estimated absolute volume transport of the Kuroshio for the upper 1,000 m (determined as the sum of geostrophic velocities of the eastward flow) varies from 34 to 91 Sv (1 Sv = 106 m3/sec). The absolute transport of the Kuroshio is found to have a very tight relationship with the difference of absolute geopotential anomalies across the Kuroshio, having a very high correlation coefficient of 0.96. This tight relationship comes from the fact that the vertical profile of the horizontally integrated transport of the Kuroshio for a unit depth, normalized by the surface layer transport, is almost constant in time; i.e., the larger (or smaller) total transport comes from larger (or smaller) transport for a unit depth in all layers. This relationship and TOPEX/POSEIDON altimetry data, which were obtained every 10 days and calibrated with those absolute geopotential anomalies, provide us for the first time with the time series of the Kuroshio transport for three years (1992-1995). The estimated transport fluctuates much around an average of 56 Sv. The annual cycle is not apparent there but some semi-annual cycle is dominated. A part of this fluctuating transport may be associated with the fluctuation of the local anticyclonic warm eddy located south of the Kuroshio. Further studies should be made to estimate the transport of the deeper layer of the Kuroshio and also the fluctuation of the transport of recirculation located south of the Kuroshio.
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