Publication Date

2009-07-24

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Applied Marine Physics (Marine)

Date of Defense

2009-07-10

First Committee Member

Mark A Donelan - Committee Chair

Second Committee Member

Brian K. Haus - Committee Co-Chair

Third Committee Member

William M. Drennan - Committee Member

Fourth Committee Member

Lynn K. Shay - Outside Committee Member

Fifth Committee Member

John C. Van Leer - Outside Committee Member

Abstract

A quantitative description of wind-wave and wind-current momentum transfer in high wind conditions is currently unresolved, mainly due to the severe character of the problem. It is, however, necessary for accurate wave models, storm and hurricane forecasting, and atmosphere-ocean model coupling. In this research, strongly forced wind-wave conditions were simulated in a laboratory tank. On the air side, a static pressure probe mounted on a vertical wave follower measured wave-induced airflow pressure fluctuations in close proximity to the surface. Vertical profiles of wave-induced pressure fluctuations were resolved and wave phase dependent features, such as airflow separation, identified. Based on the pressure measurements, wind-wave momentum fluxes were obtained. The dependence of the spectral wave growth function on wind forcing, wave steepness, and wave crest sharpness was also investigated. The bulk air-sea momentum fluxes were estimated using the "total budget" experimental technique. It provided information on the contribution of a wind-wave flux induced by a single wave to the total air-sea momentum flux. The percentile contribution of wind-wave momentum flux into one wave was found to be dependent on the wave's steepness. An arbitrary change in steepness, however, was found to modify the wave field in such a way that it had little effect on the total wind stress. To complement wind stress measurements velocity profiles in the water were measured using Particle Image Velocimetry technique. Mean current, turbulent stress, turbulent kinetic energy and turbulent dissipation rate vertical profiles were studied as a function of wind speed. Together with wave spectrum evolution measurements they form a complete empirical description of momentum fluxes in the laboratory tank. The results provide a detailed empirical view on airflow pressure fluctuations over a wavy surface, on total wind stress, and on the velocity response in the water. A new wave growth parameterization with wind forcing range extended into storm conditions is the most significant stand alone result of this work. Combined with the near surface vertical profiles, these empirical data also serve as a test bed for coupled air-sea numerical models.

Keywords

Air-Sea Interaction; Momentum Flux; High Winds; Wave Follower; Wave Growth; Wave Tank

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