07/09/2014 - 3:30pm
Buoyancy-driven coastal currents off the Oregon coast during fall and winter
Abstract: During fall/winter off the Oregon coast, oceanographic surveys are relatively scarce due to rough weather conditions. This challenge has been overcome by the use of autonomous underwater gliders deployed along the Newport Hydrographic Line (NH-Line) nearly continuously since 2006. The discharge from the coastal rivers between northern California and the NH-Line reach several thousands of m^3 /s, and peaks are comparable to the Columbia River. This freshwater input creates cross-shelf density gradients, that together with the wind-forcing and the large-scale Davidson Current, results in strong northward velocities over the shelf. A persistent coastal current during fall/winter, which we call the Oregon Coastal Current (OCC), has been revealed by the glider data set. The dominant forcing mechanism of the OCC is buoyancy, followed by the Davidson Current, and then the wind stress, accounting for 61% (+/-22.6%), 26% (+/-18.6%) and 13% (+/-11.7%) of the transports, respectively. The OCC average velocities are highly variable, from 0.1 to over 0.5 m/s, and transports are on average 0.08 (+/-0.07) Sv, with maximum observed value of 0.49 Sv, comparable to the summertime upwelling jet of the Oregon coast. The OCC is a surface-trapped coastal current and its characteristics are highly affected by the wind-stress, consistent with Ekman dynamics, which despite its small contribution to the transport, plays a primary role in modifying the OCC structure. The OCC is a persistent, key component of the fall/winter shelf dynamics and influences the ocean biogeochemistry off the Oregon coast.
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