A climatological view of the Kuroshio/Oyashio system east of Japan

Time-averaged structure of the Kuroshio/Oyashio system east of Japan was ex amined using historical hydrographic data. Unlike most of the earlier clima tological analyses, the data were averaged along isopycnal rather than pres sure surfaces in a 0.5 degrees x 0.5 degrees grid. As a result, most of the detailed phenomena associated with the narrow western boundary currents we re revealed. Water from the Oyashio is seen to overshoot the zero zonally i ntegrated wind-stress-curl line by more than 5 degrees, approaching as far south as 36 degrees -38 degreesN at the western boundary. Water from the Ku roshio Extension, by contrast, tends to feed into the Oyashio Front in the interior ocean. This exchange of waters leads to a zero of zonally integrat ed (western boundary-180 degrees) meridional transport at about 44 degreesN , reasonably coinciding with the zero of zonally integrated wind stress cur l in the western North Pacific. A well-defined double-front structure is se en at depths of the thermocline, but it does not appear to have a strong si gnature in the surface dynamic topography. Though always accompanied by str ong temperature and salinity gradients, water density changes little across the Oyashio Front near the surface. Both the Kuroshio Extension and Oyashi o Front have a significant deep component, but below 1000 m the former seem s to be dominated by eddy features associated with the Kuroshio Extension r ecirculation gyre.