Evidence of Bottom-Trapped Currents in the Kuroshio Extension Region

摘要

As part of the Kuroshio Extension System Study, observations from five current meter moorings reveal that the abyssal currents are weakly bottom intensified. In the framework of linear quasigeostrophic flow, the best fitted vertical trapping depths range from 8 to 15 km in the absence of steep topography, but one mooring near an isolated seamount exhibited vertical trapping that was more pronounced and energetic with a vertical trapping depth of 5 km. The ratios of current speeds and geostrophic pressure streamfunctions at the sea surface compared to the bottom are 88% in the absence of steep topography, 63% near an isolated seamounl, and overall on average 83% of their value at a reference depth of 5300 m. It is hypothesized that weakly depth-dependent eddies impinging upon topographic features introduce to the flow the horizontal length scales of the topography, and these smaller lateral scales are subject to bottom intensification.