Direct Current Measurements in the Frontal Zone of a Coastal Upwelling Region

Abstract

Float and flow current measurements made in September 1965 in a frontal zone associated with coastal upwelling off Oregon are described; flow measurements made the following September, with similar results, are also described. The float and flow techniques gave equivalent values for the mean flow but not for the periodic components. The frontal zone was a region of high vertical shear for both mean and periodic flows : above the frontal layer, the mean flow was usually southward and offshore; below the frontal layer, the mean flow was northward and onshore. Semidiurnal tidal currents rotated counter-clockwise above the frontal layer and clockwise below the frontal layer. Inertial period currents rotated clockwise at all depths. A temperature inversion and a speed maximum were in close proximity to the lower portion of the frontal layer. The width of the poleward subsurface flow and of the speed maximum was at least 40 kilometers. To adequately measure the dynamic structure of a frontal zone in the coastal upwelling region, we found it desirable to sample hourly for at least one lunar day at 5 or 10 meter vertical increments across the frontal layer and to make observations at 5 or 10 kilometer spacings prependicular to the coastline.