Modeling Tidal Current Profiles by Means of Empirical Orthogonal Functions

Abstract

The method of empirical orthogonal functions (EOFs) is used to model vertical velocity profiles of the current. The whole current field is decomposed into time series of along and cross-slope velocity components. These time series are then filtered keeping only the frequency bands corresponding to the most significant peaks of the current power density spectra, which in most cases correspond to the main semidiurnal and long period tidal components. New time series are originated containing only filtered current. For each one of these filtered time-series, EOFs and the respective principal components are then derived. The derivation of empirical orthogonal functions make possible the separation of the local flow variability into a few modes of variance. In a general way, the along-slope flow may be described mainly as barotropic, although the baroclinic contribution tends to reach some significance in the flow crossing the shelf slope.