RESIDUAL CURRENTS IN JUAN-DE-FUCA STRAIT

We examine the residual (non-tidal)flow in Juan de Fuca Strait on the west coast of Canada using current and bottom pressure data collected on cross-channel sections in the summers of 1975 and 1984. A positive estuarine circulation was evident in both sections but was better defi ned at the mid-strait section than at the outer section near the mouth of the strait. Magnitudes of the volume transports in both the upper and lower layers of the channel ranged from approximately 0.25 x 10(6) m3 s-1 at the mid-strait section to approximately 0.15 X 10(6) m3 s-1 at the outer section. The method of geostrophic levelling (Garrett an d Petrie, 1981; Petrie et al., 1988) is used to determine the relation ship between the daily averaged long-strait velocity component and the cross-strait pressure difference. A statistically significant relatio nship, consistent with a cross-strait geostrophic balance, is obtained between the time series of shallow currents and shallow bottom pressu res at the mid-strait section. The deep currents and cross-strait pres sure differences were correlated at both sections but, because of the placement of the pressure gauges and/or ageostrophic effects such as b ottom friction, were not related through a simple geostrophic balance. Cross-spectral analysis and the calculation of the current amplitude ratios (square root of the energy ratio between the deep and shallow c urrents) are used to examine the baroclinicity of the flow as a functi on of frequency. Results suggest that flow variability in Juan de Fuca Strait is strongly baroclinic and has marked cross-channel structure throughout the low-frequency band.