Progress on physical circulation and ecosystem modeling in the COAST and WEST programs

High resolution physical circulation and ecosystem models have been applied to study the mesoscale shelf flow field and ecosystem response off Oregon and northern California in the regions of the COAST and WEST field experiments. Localized, regional domains that extend approximately 400-600 km alongshore and 200-300 km offshore are utilized to allow high horizontal grid resolutions of 1-2 km. The Princeton Ocean Model (POM) is used for Oregon while the ROMS model is used for northern California. The Oregon ecosystem model is a five component nitrogen-based NNPZD model. In the most basic, workhorse configuration, periodicity conditions are used at the alongshore boundaries, allowing the specification of well-posed problems. For these shelf flows, where the mesoscale behavior is dominated by the interaction of wind-driven currents with variable shelf topography, that approximation leads to model results that generally show good agreement with observations. Open boundary conditions have also been developed to allow the application of spatially-variable forcing obtained from a high resolution mesoscale atmospheric model. In addition, off Oregon a data assimilation system utilizing HF-radar surface current measurements and a sequential optimal interpolation scheme is being utilized to improve estimates of the circulation. These models have been applied to the spring and summer 2001 time periods of the COAST and WEST field experiments. The modeled mesoscale shelf flow field off Oregon is strongly influenced by interactions with Heceta Bank while the flow off northern California is affected in a major way by Point Reyes. The structure of model sea surface temperature fields reflects the shelf flow interaction with these topographic features and is in good qualitative agreement with comparable satellite-measured fields. New information on the three-dimensional time-dependent nature of the velocity, temperature, and turbulent kinetic energy fields, tested with model/data comparisons where possible, is produced by the model results. Examination of model dynamical balances has helped provide rationalizations for the circulation processes responsible for the structure of these fields. In particular, analyses of model results have shown the prevalence and importance of pressure-gradient-driven northward flows near the coast after the relaxation of southward upwelling-favorable winds. More detailed accounts of the results from these modeling studies are reported at this meeting by colleagues J. Gan, Y. Spitz, S. Couch and A. Kurapov.