Uchida et al.,
Kuroshio transport south of Japan estimated from in situ oceanographic data and satellite altimeter data

KUROSHIO TRANSPORT
From moored current meter data and repeated hydrography data, geostrophic velocity field normal to the observation line, referring to velocities observed at mid and deep layers, is estimated (Fig. 3). From the velocity field, volume transport of the Kuroshio (transport of the entire eastward flow) for the upper 1,000 m is estimated. It varies from 27 to 85 Sv (1 Sv = 10^6 m^3/sec) for 25 selected hydrographic surveys (separated from each other by more than five days). The transport is found to be proportional to the sea level difference across the Kuroshio (Fig. 4a), which is related with the surface layer transport, assuming geostrophy. The relationship can be understood by the fact that the vertical profile of transport per unit depth of the Kuroshio, normalized by the surface layer transport, is almost constant in time (Fig. 4b), and therefore the total transport is proportional to the surface layer transport.

Fig. 3.
(a) Temperature section, (b) absolute geostrophic velocity section and (c) profile of the sea surface dynamic topography (SSDT) of the Kuroshio in September 1994 (R/V Hakuho-maru cruise). The velocities are calculated from hydrographic data (obtained at stations indicated by triangles) with reference to velocities observed at locations and depths indicated by dots. The SSDT profile is estimated from surface geostrophic velocities thus obtained.
Fig. 4.
Transport of the Kuroshio for upper 1,000 m. Panel (a) shows a scatter plot of the Kuroshio transport and SSDT difference across the Kuroshio. Twenty-five cases are shown. The solid line shows the regression line. The correlation coefficient is 0.90, and the root-mean-square difference from the regression line is 5.6 Sv. Panel (b) shows vertical profiles of the Kuroshio transport per unit depth, normalized by the sea-surface transport. Twenty-five individual profiles (thin line) are shown as well as the mean profile (thick line), whose standard deviation is shown by dotted lines.


[ Top | ASUKA | Kuroshio transport | Time series | Seasonal signal | References ]