| Recent high resolution hydrographic transects of the Kuroshio have revealed an energetic field of near-inertial internal waves interacting with the geostrophic flow. Near-inertial shears are large compared to geostrophic shears. Spatially coherent velocity and shear structures are observed in transects across the Kuroshio recorded during the ASIAEX Survey Program in the East China Sea in April 2000 using a Doppler Sonar System installed on the R/V Revelle. A follow-on cruise on the R/V Melville near Kyushu, Japan, in April 2002 used shipboard ADCP and lowered-ADCP to record a 30-h time series in the core of the current. CTD stations were occupied during both cruises to determine the density structure. A superimposition of near-inertial waves propagating both upwards and downwards is observed when the shear is separated in clockwise and counter-clockwise components using rotary spectral analysis. The geostrophic vorticity associated with the Kuroshio appears to act as a wall, trapping internal waves generated at the shelf break and in the Kuroshio front. Compared to the open ocean, the shear variance is increased by a factor 3 in the Kuroshio, and by a factor 6 in the region between the shelf break and the Kuroshio. Because energy dissipation has been found to scale as shear variance squared, very high values of dissipation and mixing (over 30 times the open ocean value) are expected in this area. |
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