Currents in the Juan de Fuca Strait

Abstract

The low-pass filtered residual along-strait current and across-strait pressure difference data, collected at the mid-strait and at the mouth are examined to determine the characteristics of the flow in Juan de Fuca Strait. The mean residual flow structure shows a positive estuarine circulation at both oceanographic sections.

The method of geostrophic levelling of bottom pressure gauges is tested using linear regression to determine the relationship between the along-strait residual velocities and the residual across-strait pressure differences. The regression equation shows that the south gauge is higher than the north gauge and that there is a reasonably direct relationship between the measured residual pressure difference and mean along-strait residual flow.

Cross-spectral analysis of the residual current and pressure difference time series support the geostrophic levelling results. The residual volume transport and pressure differences are coherent in only the lowest frequency band with the two time series out of phase by $\approx$180$\sp\circ$. The residual across-strait pressure differences are a good measure of the mean along-strait surface currents but only a fair measure of the net volume transport.

The amplitude ratio shows a slight increase with increasing frequency at the mid-strait section but the trend is not smooth. (Abstract shortened by UMI.)