The University of Southampton
University of Southampton Institutional Repository

The refraction, shoaling and structure of non-linear internal waves at a continental shelf margin

The refraction, shoaling and structure of non-linear internal waves at a continental shelf margin
The refraction, shoaling and structure of non-linear internal waves at a continental shelf margin
Observations of internal waves near the Continental shelf-edge are generally ascribed to generation by oscillating tidal flow over the local bathymetry, in the presence of a stratified water column, giving rise to the internal tide. In this thesis observations are presented which demonstrate that internal waves at the Malin shelf-edge comprise of both the locally generated internal tide, and waves from a distant source. This thesis focuses on processes affecting the latter phenomenon at the continental slope. A comprehensive collection of in-situ and satellite data from the Shelf Edge Study (SES) and the Shelf Edge Study Acoustic Measurement Experiment (SESAME) from August-September 1995 and August1996 is used to describe the internal wave characteristics. During a period of neap tides a set of internal solitary waves was tracked across the continental slope every tidal cycle for three days. The measurements indicate that the waves evolved from an initial drop in the thermocline, and were not significantly refracted as they crossed the slope, due to the small change in phase speed across the slope, from around 0.8 to 0.6 m/s. The internal waves depressed the thermocline by between 30 and 50 m and had particle speeds of 0.4 to 0.8 m/s. The structure of the internal waves is examined and compared to weakly non-linear theory, and it is found that first order theory adequately describes the waves over the slope but that a second order theory is required to model the internal waves on the shelf. A non-linear refraction model is developed to simulate the internal wave propagation and evolution. Initial tests of the model for the refraction and shoaling of interfacial solitary waves propagating in simple environments show agreement with analytical results. The model is then extended to simulate the refraction and transformation of the internal waves observed during SES, using realistic density stratification and bathymetry. When realistic initial conditions derived from measurements are used, it is found that the model reproduces the phase speeds and refraction characteristics very well, but overestimates wave amplitudes at the shelf-edge and the shelf. Analysis of the simulated internal waves suggests that the waves would become unstable at these amplitudes and would in reality be damped. In fact it is shown from the observations that instabilities in the wave are likely to occur due to the high shear and high particle speed relative to the phase speed, and an example of possible breaking internal waves is illustrated. The likely regions of non-linear internal wave dissipation are considered in the Discussion, together with the local generation of internal tides, and possible source regions for the distant internal waves.
Small, R.J.O.
5978ad84-6a47-487a-9a70-581659c13225
Small, R.J.O.
5978ad84-6a47-487a-9a70-581659c13225

Small, R.J.O. (2000) The refraction, shoaling and structure of non-linear internal waves at a continental shelf margin. University of Southampton, Faculty of Science, School of Ocean and Earth Science, Doctoral Thesis, 280pp.

Record type: Thesis (Doctoral)

Abstract

Observations of internal waves near the Continental shelf-edge are generally ascribed to generation by oscillating tidal flow over the local bathymetry, in the presence of a stratified water column, giving rise to the internal tide. In this thesis observations are presented which demonstrate that internal waves at the Malin shelf-edge comprise of both the locally generated internal tide, and waves from a distant source. This thesis focuses on processes affecting the latter phenomenon at the continental slope. A comprehensive collection of in-situ and satellite data from the Shelf Edge Study (SES) and the Shelf Edge Study Acoustic Measurement Experiment (SESAME) from August-September 1995 and August1996 is used to describe the internal wave characteristics. During a period of neap tides a set of internal solitary waves was tracked across the continental slope every tidal cycle for three days. The measurements indicate that the waves evolved from an initial drop in the thermocline, and were not significantly refracted as they crossed the slope, due to the small change in phase speed across the slope, from around 0.8 to 0.6 m/s. The internal waves depressed the thermocline by between 30 and 50 m and had particle speeds of 0.4 to 0.8 m/s. The structure of the internal waves is examined and compared to weakly non-linear theory, and it is found that first order theory adequately describes the waves over the slope but that a second order theory is required to model the internal waves on the shelf. A non-linear refraction model is developed to simulate the internal wave propagation and evolution. Initial tests of the model for the refraction and shoaling of interfacial solitary waves propagating in simple environments show agreement with analytical results. The model is then extended to simulate the refraction and transformation of the internal waves observed during SES, using realistic density stratification and bathymetry. When realistic initial conditions derived from measurements are used, it is found that the model reproduces the phase speeds and refraction characteristics very well, but overestimates wave amplitudes at the shelf-edge and the shelf. Analysis of the simulated internal waves suggests that the waves would become unstable at these amplitudes and would in reality be damped. In fact it is shown from the observations that instabilities in the wave are likely to occur due to the high shear and high particle speed relative to the phase speed, and an example of possible breaking internal waves is illustrated. The likely regions of non-linear internal wave dissipation are considered in the Discussion, together with the local generation of internal tides, and possible source regions for the distant internal waves.

Text
0000393.pdf - Other
Download (23MB)

More information

Published date: June 2000
Additional Information: Digitized via the E-THOS exercise.
Organisations: University of Southampton

Identifiers

Local EPrints ID: 42171
URI: https://eprints.soton.ac.uk/id/eprint/42171
PURE UUID: 372f5a4f-5c79-4c86-88fc-c115c2cfea09

Catalogue record

Date deposited: 22 Nov 2006
Last modified: 13 Mar 2019 21:12

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×