Investigations of the Poleward Undercurrent Over the Continental Margin Along the Ocean's Eastern Boundaries

摘要

Our goal is to determine the characteristics of poleward undercurrents, which are ubiquitously observed along the eastern margin of ocean basins, including their strength, structure, and variability, and to understand the dynamics controlling them. The objective of the present effort is to determine the velocity field and its mesoscale variability along the continental margin off North America, from Point Conception, California, to Vancouver Island, Canada, during the summer of 1998. In July-August 1998, ADCP data were acquired during the triennial NOAA NMFS acoustic and trawl survey of Pacific whiting, which extended from 36 degrees N to 52 degrees N. Such a survey, while not synoptic along its whole domain, is locally synoptic, since integral time scales over the continental slope are typically 4 to 10 days, as observed with the Eastern Boundary Currents moored array. Vertical profiles of ocean currents were collected during both legs of the Triennial Trawl Survey, using a downward-looking 150-kHz ADCP installed on the NOAA ship 'Miller Freeman.' Because bottomtracking data were not available (the bottom-tracking pings interfered with the acoustics used in the fish assessments), all profiles were hand-screened for bottom interference before further processing. Absolute currents were computed using differentially-corrected GPS data, after calibration and misalignment corrections were determined from the differences between on-station and underway currents. Preliminary maps of currents at fixed depths through the poleward undercurrent have been made.