Publication Date

2008-12-22

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Applied Marine Physics (Marine)

Date of Defense

2008-11-16

First Committee Member

William M. Drennan - Committee Chair

Second Committee Member

Hans C. Graber - Committee Member

Third Committee Member

Brian K. Haus - Committee Member

Fourth Committee Member

Peter J. Minnett - Committee Member

Fifth Committee Member

Kimmo K. Kahma - Committee Member

Abstract

This dissertation investigates wind-wave-current interaction, wave breaking detection and the analysis of breaking characteristics at the air-sea interface. In-situ data measured during the Shoaling Waves Experiment (SHOWEX) and Baltic Sea Swell Experiment (BASE) are applied in the studies and analysis. Wind, wind stress and wave data were obtained from several Air Sea Interaction Spar (ASIS) buoys. Surface currents were measured by a High-Frequency Ocean Surface Current Radar. Two distinct types of wave-current-wind interaction were observed in the presence of a strong along-coast current. First, the horizontal current shear resulted in wind-sea waves shifting away from the wind direction. This motion resulted in a steering of the stress away from the mean wind direction. Second, short wind waves on a uniform current are shifted to the current direction, and the wind stress is steered toward the current direction by the short waves. The wind stress veering has been confirmed by data from the SeaWind scatterometer on board the QuikSCAT satellite. This finding is in agreement with the results from some recent studies. The present study also describes an experimental investigation of breaking wave detection by ASIS buoys. A method, developed from the laboratory, and using local wave parameters to provide a detailed description of breaking, is applied to wave data from ASIS buoys. One the basis of these data, the relation between breaking probability and wind speed shows characteristics similar to those from several field experiments with different conditions. Furthermore, additional parameters, wave age and wave steepness, are also shown to affect the breaking probability during our in-situ measurements. Upper ocean shear, which can modulate wave breaking as predicted by both theory and laboratory work, are also observed to change the breaking properties. This characteristic is rarely reported by in-situ experiment.

Keywords

Air-sea Interaction; Wind Stress; Wave; Current

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