THE PROPAGATION OF HIGH-FREQUENCY INTERNAL WAVES IN THE CELTIC-SEA

The continental slope to the south of the Celtic Sea is an area of ext remely rough topography and tidal currents of the order of 50cm/s (wit h components both along and across the slope). This is a region of int ense and complicated internal wave and internal tide activity. Histori cal current meter data from moorings close to the shelf-break show bur sts of high frequency, large amplitude internal waves occurring, on av erage, at either once or twice per M2 tidal cycle. Wave packets at 9 m oorings along the shelf-break and further on-shelf are identified usin g conditional sampling. The paths travelled by these wave packets are calculated using their fluctuation orientation, linear wave theory and the low frequency current. The records are up to 60 days long, allowi ng the ensemble statistics of propagation direction and wave character istics to be calculated for a large number of wave packets. This analy sis shows that only a fraction of the observed wave packets have orien tations consistent with generation by the across-slope barotropic tide . This mechanism accounts for 20% of the wave packets in the north-wes t Celtic Sea and 29% in the southeast Celtic sea. A similar fraction o f the wave packets (23% in the north west and 27% in the south east) h ave orientations clearly consistent with generation by an along-slope flow over the rough topography on the slope. The remaining wave packet s are attributed to generation by tidal flow over topography close to the moorings and possibly internal wave resonance within canyons. (C) 1998 Elsevier Science Ltd. All rights reserved.