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Time-Varying Across-Shelf Ekman Transport and Vertical Eddy Viscosity on the Inner Shelf

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https://ir.library.oregonstate.edu/concern/articles/kk91fn086

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Abstract
  • The event-scale variability of across-shelf transport was investigated using observations made in 15 m of water on the central Oregon inner shelf. In a study area with intermittently upwelling-favorable winds and significant density stratification, hydrographic and velocity observations show rapid across-shelf movement of water masses over event time scales of 2–7 days. To understand the time variability of across-shelf exchange, an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum from velocity profiles and wind forcing. Depth-averaged eddy viscosity varied over a large dynamic range, but averaged 1.3 X 10⁻³ m² s⁻¹ during upwelling winds and 2.1 X 10⁻³ m² s⁻¹ during downwelling winds. The fraction of full Ekman transport present in the surface layer, a measure of the efficiency of across-shelf exchange at this water depth, was a strong function of eddy viscosity and wind forcing, but not stratification. Transport fractions ranged from 60%, during times of weak or variable wind forcing and low eddy viscosity, to 10%–20%, during times of strong downwelling and high eddy viscosity. The difference in eddy viscosities between upwelling and downwelling led to varying across-shelf exchange efficiencies and, potentially, increased net upwelling over time. These results quantify the variability of across-shelf transport efficiency and have significant implications for ecological processes (e.g., larval transport) in the inner shelf.
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  • Kirincich, Anthony R., John A. Barth, 2009: Time-Varying Across-Shelf Ekman Transport and Vertical Eddy Viscosity on the Inner Shelf. J. Phys. Oceanogr., 39, 602–620.
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  • 39
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  • 3
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  • This paper is Contribution Number 310 from PISCO, the Partnership for Interdisciplinary Studies of Coastal Oceans, funded primarily by the Gordon and Betty Moore Foundation and the David and Lucile Packard Foundation.
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