Direct current measurements of the Kuroshio were carried out from September 1993 to November 1995 by using moored current meters along an observation line extending over 800 km long from Cape
Ashizuri of Shikoku, Japan to the south-southeast. The line coincides with a track of the altimeter satellite Topex/Poseidon (T/P). 33 Aanderaa current meters (CM) were deployed at nominal depths of 700
m, 1500 m and 3000 m, and just above the continental slope on nine mooring stations along the observation line to study the detailed subsurface structure and variability of the Kuroshio. During these CM
observations period, hydrographic surveys (CTD) were carried out 42 times along the line. The results from these surveys are combined with those from CM measurements. The observations were a part of
Affiliated Surveys of the Kuroshio off Cape Ashizuri (ASUKA), which was planned to estimate the net meridional heat transport of the subtropical gyre of the North Pacific, being combined with the
trans-Pacific hydrographic survey along 30 °N line.
The strongest part of the Kuroshio at 650 m depth is found to exist at the position of the water temperature of 7 °C at the same depth. Accordingly, we use this position of temperature as
the axis of the Kuroshio stream at this depth.
The geostrophic balance in the Kuroshio region is examined using CM and CTD data. The five-day mean vertical shears of horizontal velocity estimated from CM data compare best with geostrophic shears calculated from CTD
data.
To understand the fluctuation of the volume transport of the Kuroshio, we calculate the
transports per unit depth (TPUD) at two mid-depths, 650 m and 1500 m, and at the sea surface. We estimate the TPUD by integrating the velocity components normal to the ASUKA-line from the coast to the offshore edge of eastward flowing surface Kuroshio, which is determined from T/P altimeter data. The TPUD varies from about 20 to 70 Sv/km at 650 m depth and from -5 to 20 Sv/km at 1500 m
depth, estimated from CM data. It varies from 60 to 170 Sv/km at the surface, estimated from the altimeter data. The correlation coefficient of TPUD between the sea surface and the 650 m depth is very high, 0.92, but those between the others are not meaningfully high.
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