A Climatological View of the Kuroshio/Oyashio System East of Japan*

Time-averaged structure of the Kuroshio/Oyashio system east of Japan was examined using historical hydrographic data. Unlike most of the earlier climatological analyses, the data were averaged along isopycnal rather than pressure surfaces in a 0.58 3 0.58 grid. As a result, most of the detailed phenomena associated with the narrow western boundary currents were revealed. Water from the Oyashio is seen to overshoot the zero zonally integrated wind-stress-curl line by more than 58, approaching as far south as 368–388N at the western boundary. Water from the Kuroshio Extension, by contrast, tends to feed into the Oyashio Front in the interior ocean. This exchange of waters leads to a zero of zonally integrated (western boundary–1808) meridional transport at about 448N, reasonably coinciding with the zero of zonally integrated wind stress curl in the western North Pacific. A well-defined double-front structure is seen at depths of the thermocline, but it does not appear to have a strong signature in the surface dynamic topography. Though always accompanied by strong temperature and salinity gradients, water density changes little across the Oyashio Front near the surface. Both the Kuroshio Extension and Oyashio Front have a significant deep component, but below 1000 m the former seems to be dominated by eddy features associated with the Kuroshio Extension recirculation gyre.