Rotary Empirical Orthogonal Function Analysis of Currents near the Oregon Coast

Abstract

Abstract Empirical orthogonal function (EOF) analysis in the frequency domain is extended to complex time series. EOFs are calculated from the eigenvectors of the band-averaged rotary cross-spectral matrix. This gives EOF amplitude and phase for negative and positive frequencies, corresponding to clockwise and anticlockwise rotation for the hodograph model. Rotary EOF analysis is applied to velocity and temperature measurements from the Coastal Upwelling Experiment (CUE-II) during July and August 1973 on the continental shelf off Oregon. Rotary EOFs for horizontal velocities are computed for the diurnal, near-inertial and semidiurnal frequency bands (approximately 1.0, 1.5 and 2.0 cycles per day, respectively) and for frequency bands below 0.3 cycles per day. In addition, single-sided frequency-space EOFs for vertical displacement are calculated from temperature measurements. The first-mode velocity EOF for the semidiurnal frequency band shows baroclinic structure for clockwise rotation and barotropic str...