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Structure of the coastal current field off Northern California during the coastal ocean dynamics experiment

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https://ir.library.oregonstate.edu/concern/articles/8336h700n

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  • For 74 days during the spring and summer upwelling seasons of 1981 and 1982, in conjunction with the Coastal Ocean Dynamics Experiment, profiles of upper ocean currents were collected in the waters over the shelf and slope off northern California using a shipboard Doppler acoustic log. These measurements provide detailed information on the spatial structure of the current field. Synoptic maps of near-surface currents often deviate substantially from classical two-dimensional wind-driven upwelling and indicate a close association between the complex temperature structures observed in satellite imagery and the presence of vigorous current structures including squirts (regions of intense seaward flow), eddies, and countercurrents. Well-defined examples of a squirt and of a countercurrent during a cessation of wind forcing (wind relaxation event) are examined in detail. Despite this complexity, the nearshore synoptic current field was found to be anisotropic, varying more rapidly cross shore than alongshore. The structure of the current averages and simple fluctuation statistics were largely as deduced in other upwelling areas from moored measurements. A surface-intensified equatorward jet was found in the average alongshore currents, with vertical shear exceeding -2 x 10^(-3) s^(-1) over much of the shelf. The core of the jet moved offshore south of Point Arena and was better resolved in along-isobath averages. At depths below 80 m the average alongshore flow reversed, giving way to a poleward undercurrent, strongest near the shelf break. The detailed structure of the inferred cross-shore circulation was found to be sensitive to the coordinate system selected. Using nominal (along-coast) coordinates, the average cross-shore current was found to be directed offshore within a surface layer which deepened with distance from the coast out to the shelf break, showed strong vertical shear only near the surface, and was divergent in the upper water column and convergent in the lower water column over the shelf. Current fluctuations about the local mean were strongly polarized along isobaths near the coast and became largely isotropic far from shore except offshore from Point Arena, where squirts were recurrently observed.
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  • Kosro, P. M. (1987). Structure of the coastal current field off Northern California during the coastal ocean dynamics experiment. Journal of Geophysical Research, 92(C2), 1637-1654.
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  • 92
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  • C2
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  • National Science Foundation grants OCE-8410546 and OCE-8410861.Office of Naval Research grant N00014-80-C-0440.
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