Diurnal variability in currents and temperature on the continental shelf between central and southern California

Abstract

Long time series are used to describe the diurnal variability in the meteorological and astronomical tidal forcing and the temperature and current response on the continental shelf of California between Port San Luis and Port Hueneme. Spectral characteristics are used to attribute the response to each of the forcing mechanisms. The diurnal temperature field is decomposed into two dominant vertical modes. A surface-enhanced mode is coherent with the meteorological forcing, suggesting that it is a direct response to local heating and wind forcing. The amplitude of the second mode is maximum at middepth. Spectra of this mode exhibit multiple peaks at frequencies corresponding to the astronomical tidal forcing. The phase difference between the middepth mode and the tidally dominated sea level is not consistent across the region. We conclude that this mode is a localized baroclinic response to the astronomical tidal forcing. The diurnal velocity field is dominated by a clockwise component. At the surface this component is coherent across the study region, and it is also coherent with the diurnal wind stress, suggesting that it is a direct response to the diurnal heating and wind forcing. Coherence with the surface-enhanced temperature mode further confirms this. A weaker, barotropic counterclockwise component is also present in the diurnal velocity field. Spectra of this component exhibit multiple peaks at periods corresponding to the astronomical tidal forcing. The phase difference between this component and the surface elevation varies little between the observational sites. We conclude that this velocity component represents a barotropic response to astronomical forcing that is coherent over the study area. Copyright 2005 by the American Geophysical Union.