Abstract
Abstract. Observations of internal waves were made at the Malin shelf edge during SESAME (Shelf Edge Studies Acoustic Measurement Experiment), a part of the NERC LOIS-SES experiment, in August-September 1996. These measurements provide a high resolution dataset demonstrating internal wave generation and propagation. This note presents observations of the evolution of an internal bore. The process is shown clearly in a sequence of thermistor chain tows across the shelf break covering a complete tidal cycle, as the double-sided bore transforms into a group of undulations and eventually into more distinct solitary waveforms. Current structures associated with the bore and waves were also observed by ship-mounted ADCP. Analysis of the waveforms in terms of the linear modes and empirical orthogonal functions (EOFs) indicate the dominance of the first mode, which is typical of a shallow water seasonal thermocline environment. Determination of the phase speed of the waves from the consecutive ship surveys enabled the Doppler shift in the towed data to be removed, allowing analysis of the real length scales of the waves. The bore evolution has been modelled using a first order non-linear KdV model for the first mode, initialised with the waveform in the first survey. Comparison of the model and the observations show close agreement in the amplitudes, length scales, phase speeds and separations of the leading internal waves as they evolve. Finally, analysis of the observed internal wave shapes indicates that, within the uncertainties of measurement, the wave-lengths lie between those predicted by first and second order soliton theory.Key words. Oceanography: general (continental shelf processes; ocean prediction). Oceanography: physical (internal and inertial waves)
Highlights
Internal bores and high frequency internal waves are a common phenomenon at regions of varying topography such as shelf breaks (Huthnance, 1989; Ostrovsky and Stepanyants, 1989)
)0.1c0 respectively for a wave of amplitude )28 m in water depth 150 m (a/h 0.2 in GG terminology), and c ÿ0:013. This implies that the second order half width is 1.56 times the ®rst order estimate, and the phase speed is reduced from the Korteweg and de-Vries (KdV) prediction by 0.1 times the linear speed, and the wave is very slightlyattened in shape
Thermistor chain records showed the thermoclineuctuations to high resolution, while ADCP records indicated the current structure at a coarser resolution
Summary
Internal bores and high frequency internal waves are a common phenomenon at regions of varying topography such as shelf breaks (Huthnance, 1989; Ostrovsky and Stepanyants, 1989). Indicate these internal tide period waves are usually accompanied by higher frequency internal waves, typically in the 10 min±1 h period range. These features are commonly seen in remotely sensed data such as high-resolution imaging radar images from Synthetic. Current research into high frequency internal waves includes analysis using more non-linear, extended KdV type equations (Lamb and Yan, 1996), and investigation of the role of energy supply and dissipation (Henyey and Hoering, 1997). The data shows clearly the evolution of an internal bore into a set of high frequency waves, allowing analysis of the evolution of the waves
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
