Langmuir circulation : a side-scan sonar study of mixing in Loch Ness

Curé, Marcel Serge (1994) Langmuir circulation : a side-scan sonar study of mixing in Loch Ness. University of Southampton, Doctoral Thesis.

Abstract

Three experiments, each of one month duration, in the spring, autumn and late winter, have been conducted in Loch Ness Scotland. Side-scan sonars, placed on the bottom, inverted and directed across the loch and dominant wind direction have been used to observe breaking waves, the clouds of bubbles produced by them and the effect of Langmuir circulation in organising these clouds into bubble bands aligned more or less down wind. Sonar data is digitally processed to reveal 'skeletons', lines showing the time development of the positions of surface convergences. These reveal a dramatic variation in the cross wind position of Langmuir cells, which increases with wind speed. Statistics are derived to describe this, the scale, lifetime penetration and convergence speeds into Langmuir cells.

The initial scale between convergences of Langmuir cell, which forms when a wind arises after a calm, is found to be far smaller (� 1 m) than has been previously observed. The Craik-Leibovich theory proves inadequate to predict the details of cell formation. Some other periods chosen for study show the rapid destruction and reformation of bubble bands following strong wind gusts and following a sustained drop in wind speed, the near constant scale and strength of Langmuir circulation and frequency of wave breaking. Video pictures of wind-rows show them to usually, but not always, to coincide with bubble bands. Side-scan sonar shows how Langmuir cells are drawn into a small scale frontal convergence. The frontal convergence position is found to be displaced from the line surface line of maximum temperature gradient. (DX183778)

This record has no associated files available for download.

Contributors

Download statistics