Numerical modeling of the Juan de Fuca eddy

Amy MacFadyen¹, Michael G.G. Foreman², Barbara M. Hickey¹

1 University of Washington, School of Oceanography, Seattle, WA, 98195, USA
EMAIL: amoreena@ocean.washington.edu
2 Department of Fisheries and Oceans, Institute of Ocean Sciences, Sidney, BC, V8L 4B2, Canada

The counterclockwise cold eddy off the Strait of Juan de Fuca has been implicated as an initiation site for toxic Pseudo-nitzschia cells. A diagnostic finite element circulation model was developed for this region and the northern Washington shelf. When forced with summertime temperature and salinity measurements, tides and typical summer winds, the model circulation shows strong retention in the eddy region and model drifter trajectories compare well with true drifters released in 2001 through 2003. Both model and true drifter trajectories show that surface waters tend to leave the eddy to flow southeastward along the Washington shelf. During storms onshore Ekman surface flow moves drifter pathways closer to the coast suggesting that phytoplankton from the surface waters of the Juan de Fuca eddy could impact the Washington coast.
Initialization of a prognostic numerical model (ROMS) is also underway. This model will both provide flow fields for a biological model and be used for process studies looking at the dynamics of the eddy itself. This model will also be used to further examine the transport of HABs to the coast, working towards a forecasting ability when forced by the UW MM5 atmospheric model.