Semidiurnal internal tides in eastern Bass Strait

Variations in the vertical thermal structure near the shelf break in eastern Bass Strait have been observed for a 1-year period during 1980-1981. For the periods when the water column was stratified, energetic oscillations of the thermocline were frequently observed, these being well correlated with the surface tide. A peak occurred at the semidiurnal frequency in approximately half of the spectra, each constructed from 4 days of thermistor records. The amplitude of this internal tide was up to 40 m from crest to trough in February 1981. The internal tide lagged the surface tide by 0-6 h in the five records analysed for phase. This, together with the consistency of phase in longer records, supports the proposal that these internal -motions were due to forcing not far from the site of observation. It is suggested that to popographic forcing can be scaled on the parameter h-2 δh/δx, where h is water depth and x is measured perpendicular to the isobaths, and a map of this parameter shows a line of strong generation near the 100-m isobath, about 10 km from our measurement site.