Modeling the mesoscale eddy field in the Gulf of Alaska

Mesoscale anticyclonic eddies are a common feature in the Gulf of Alaska (GOA). A three-dimensional circulation model is used to examine the general characteristics of eddies in the GOA during 1993–2009. Using an eddy detection algorithm, we tracked on average 6.5 eddies formed each year from the modeled results and 6.9 eddies from altimeter data. Modeled eddy characteristics agree with the remote sensing derived eddy statistics in terms of eddy magnitude, propagation speed, and eddy-core diameter. From the model results, strong seasonal and interannual variations were found in both the number and areal coverage of GOA eddies. At the seasonal scale, more eddies are observed to form from March to May, while the eddy-covered area usually peaks around October. At the interannual scale, our results suggest the years with large eddy-covered area do not necessarily have more eddies generated. The long-term variation of eddy-covered area in the GOA is modulated by El Niño/Southern Oscillation (ENSO) events through altering the local wind stress. Model results indicate one typical Haida eddy could transport 37×1018 J of heat and 27 km3 of freshwater from the shelf to the central gulf. The equivalent fluxes caused by Haida eddies are comparable with the annual mean of net heat flux and freshwater flux from the atmosphere into the ocean in the Haida region, implying that mesoscale eddies are important sources contributing to the heat and freshwater budgets.