Modal Decomposition of the Velocity Field near the Oregon Coast

Abstract

Abstract The low-frequency [ω<0.5 cycle per day (cpd)] current fluctuations at four depths in 100 m of waterhave been investigated for two stations on the continental shelf off the coast of Oregon. One station, DB-7,was maintained during the summer of 1972 as part of the Coastal Upwelling Experiment-1 (CUE-I), and theother station, Carnation, was maintained during the summer of 1973 as part of CUE-II. A decomposition ofthe north-south (almost alongshore) v and the east-west (onshore-offshore) u components of the current hasbeen performed in terms of two types of modal structures in the vertical direction: (i) dynamic modes determined by the separable solutions of the appropriate equations of motion, and (ii) empirical orthogonal modeswhich are the eigenvectors of the correlation matrix and depend only on the statistics of the data. For thealongshore currents, the standard deviation of the dynamic barotropic mode is found to be twice as large asthat of the first baroclinic mode. The barotropic part is foun...