Coastal Ocean Processes (CoOP) Begins West Coast Program

Circulation and Ecosystem Modeling for the Oregon Coast (Allen, J. [Oregon State University]) The general objective of this project is to understand and be able to model physical oceanographic circulation processes and accompanying ecosystem dynamics in the wind-forced continental shelf flow fields off the U.S. northwest Pacific coast. Immediate objectives include the application of high resolution numerical circulation and ecosystem models to both process studies and to direct simulations of continental shelf and slope flow fields for investigations of the physical and biological mechanisms involved in wind-forced across-shelf transport processes. A specific goal is to develop the capability to support future Coastal Ocean Processes (CoOP) program field experiments with application of a high resolution, limited-area, regional shelf circulation and ecosystem model. That model would be used to help understand the physical and biological processes in the observed flow fields by providing interpolation or extrapolation of necessarily incomplete measurements and by enabling directly relevant process studies.

The research plan involves application of a high resolution three-dimensional, numerical model for the hydrostatic primitive equations to studies of flow on the Oregon continental shelf and slope. The initial application will be with the Blumberg-Mellor (1987) finite difference, sigma coordinate model. The ecosystem model of Moisan and Hofmann (1996) will be parameterized for the Oregon shelf and coupled to the physical primitive equation model. Planned model domains will extend 300-400 km alongshore and 150-200 km offshore, with horizontal grid sizes of 1 km or less and 40 or more vertical sigma levels. The domain will thus cover most regions of coldest shelf mesoscale variability induced by alongshore topographic or wind stress irregularities and, correspondingly, will cover the regions of typical field experiments. Open boundary conditions for the circulation model will be formulated based on experience gained from work in progress on a model for the northern California shelf in the region of the Coastal Ocean Dynamics Experiment (CODE). The initial model domain will include a region of the continental shelf off Oregon from approximately 42°N to 45.5°N. This region includes ideal potential locations for future Coastal Ocean Process (CoOP) field experiments. In addition, previous and ongoing field experiments in this region provide both physical and biological measurements necessary for initial model comparisons.

Proposed research involves investigations of three-dimensional wind-forced circulation processes and ecosystem dynamics in both upwelling (summer) and downwelling (winter) regimes through numerical experiments involving process studies and direct simulations. Physical model results of the direct simulations will be compared to existing measurements through calculations of appropriate statistical and joint statistical functions. The initial objective is to find the requirements on the use of the models to properly represent the important physical and biological features observed in previous field experiments. Physical oceanographic investigations will focus on the time-dependent, three-dimensional dynamics of the following processes which potentially play major roles in the across-shelf circulation; upwelling and downwelling fronts, surface and bottom boundary layer behavior including the role of the turbulence parameterization schemes and the nature of bottom layer behavior including the role of downwelling conditions, and interactions of the wind forced flow field with variations in shelf topography and coastline geometry. Particular attention will be given to model studies of the flow near Cape Blanco (43°N) where separation of the southward coastal jet on the shelf has been observed during summer.

Ecosystem studies will focus initially on experiments in flows utilizing a two dimensional approximation (variation across-shelf and with depth; uniformity alongshore) as a desirable prerequisite to experiments in more complex dimensional flow fields and for calibration purposes, e.g., for determination of optimum representations for growth and death rates. Objectives include determination of the ecosystem response during both upwelling and downwelling under conditions of time varying wind forcing. Investigations of ecosystem dynamics in the three-dimensional shelf and slope flow experiments mentioned above will follow.