Reflection of the Internal Tide in Upper Loch Linnhe, a Scottish Fjord

Results from an observational study of the internal tide of Upper Loch Linnhe, a fjord on the west coast of Scotland, are presented. Between November 1992 and June 1993, moorings containing current meters measuring velocity, temperature and salinity were deployed at two sites in the loch. Observations of the horizontal velocities show the presence of an energetic first mode linear internal tide at the M2frequency with surface amplitudes of up to 0•57 m s−1(cf. 0•03 m s−1for the barotropic component). Independent evidence of the M2internal tide is provided by vertical velocities inferred from salinity and temperature variations. In June 1993, an undulating CTD was used to study the horizontal propagation of the semi-diurnal internal tide. The results show that over the inner reaches of the loch, the internal tide behaves as a standing wave, with a large proportion of the internal tide energy being reflected at the landward end of the loch. Using the phase relationship between the velocity components from the mooring data, it is demonstrated that there is a significant standing-wave component present throughout the 7-month observational period. Closer to the sill, the undulating CTD observations show the formation of an intense hydraulic jump on the flood tide, suggesting the area immediately landward of the sill to be a region of complicated dynamics and high dissipation.