Observations of Energetic Internal Waves in and Under the Kuroshio

Western boundary currents have been studied for a long time, although most of the work has been done in measuring the mean structure and mean transport. Observations obtained as part of the ASIAEX Program in Spring 2000 pointed out the presence of highly coherent "small" shear structures in the Kuroshio. The geostrophic shear associated with the Kuroshio front constituted less than half of the observed rms shear, the majority being associated with large baroclinic wavelike features found in and under the core of the current. To further investigate the nature and importance of these structures, new hydrographic and velocity measurements of the Kuroshio were taken in April 2002 South-East of Kyushu. Both shipboard and lowered-ADCP were used to measure the current. Several transects were obtained as well as a 30-h time series in the core of the Kuroshio. Energetic shear structures were again seen and appeared to propagate across isopycnals. The geostrophic vorticity at the site significantly modifies waves generated both locally and remotely. Dynamical models of the Kuroshio must account for the dissipative aspects of these very high shear wave groups.