Analysis of the influence of internal waves of tidal period upon the mixed-layer depth.

Abstract

The apparently random oscillation of the mixed-layer depth is investigated and, by the nature of its energy spectrum and its correlation with tidal activity, a determination of the source of some components of this oscillation is made. Actual and smoothed values of the mixed-layer depth at ocean station "P" in the Gulf of Alaska are subjected to spectral analysis for the presence of suspected tidal periodicities. To locate the source of the tidal influences, correlations between tidal activity on the shelf and a measure of the magnitude of the oscillation of the mixed layer at "P" are found for various lags. The amplitudes of the oscillations observed at the ocean station are compared to those calculated from a model proposed by Rattray. The spectrum analysis shows large energy peaks at tidal periodicities. The close agreement, especially in the winter season, between the lag for large correlation of the tidal activity at the shelf with the mixed-layer depth oscillation at "P" and calculated travel times of the internal tide from the shelf to "P" suggest that the generation of the internal tide is at the continental shelf.