A Modeling Study of the Three-Dimensional Continental Shelf Circulation off Oregon. Part I: Model–Data Comparisons

Abstract

Sixty-day simulations of the subinertial continental shelf circulation off Oregon are performed for a hindcast study of summer 1999. Model results are compared with in situ currents, high-frequency radar‐derived surface currents, and hydrographic measurements obtained from an array of moored instruments and field surveys. The correlations between observed and modeled alongshore currents and temperatures in water depths of 50 m are in excess of 0.8. A study designed to test the model’s sensitivity to different initial stratification, surface forcing, domain size, and river forcing demonstrates that surface heating is important, and that the model results are sensitive to initial stratification. An objective criterion for assessing the skill of a model simulation relative to a control simulation is outlined, providing an objective means for identifying the best model simulation. The model‐data comparisons demonstrate that temperature fluctuations off Newport are primarily in response to surface heating and that subsurface density fluctuations are controlled by the wind-forced circulation through salinity. Experiments with river forcing indicate that, in the vicinity of Newport, the Columbia River plume is typically greater than 15 km from the coast and is confined to the top few meters of the water column. Additionally, the model‐data comparisons suggest that the strongest upwelling occurs to the north of Newport where the continental shelf is relatively narrow and uniform in the alongshore direction. Part II of this study investigates the modeled three-dimensional circulation and dynamical balances. A numerical modeling study of the coastal ocean circulation off Oregon during the 1999 upwelling season is presented. The model results are compared with in situ velocity, temperature and salinity measurements, and high-frequency (HF) radar‐derived surface currents obtained during summer 1999 as a part of the Oregon State University (OSU) National Oceanographic Partnership Program (NOPP) project. The aims of this study are to assess the performance of the model, to identify the dominant physical processes, and to assess the model’s sensitivity to variations in initial stratification, surface forcing, model domain size, and river forcing. Processes that are of particular interest in this study include the response to wind forcing and the generation of the northward flow that is commonly observed off Newport (44.658N) over the