Date of Award


Degree Type


Degree Name

Master of Science in Oceanography



First Advisor

Tetsu Hara


The experimental data from the Risø Air-Sea Experiment (RASEX) and the Marine Boundary Layers (MBL) experiment are used to investigate the nonlinear coupling effects among different frequency components in surface wave field under both fetch-limited finite depth conditions and open ocean conditions. The wavenumber-frequency spectra are calculated using the Maximum Likelihood Method (MLM). The reliability of the MLM is tested using computer-simulated wave fields. The frequency power spectra from the shallow water RASEX experiment reveal that the slopes of the equilibrium range are close to the f-4 dependence. On the other hand, the equilibrium range spectra from the open-ocean MBL experiment follow a steeper f-5 power law. The wavenumber-frequency spectra of developed wave fields from the open ocean suggest that the bulk of wave energy at higher frequencies belongs to the higher bound harmonics of the dominant waves rather than to freely propagating waves. This finding is further supported by the bispectral analysis that shows significant phase coupling between the dominant waves and a wide range of high frequency components. In contrast with the open ocean, the wave fields under fetch limited finite-depth conditions show phase coupling only at discrete frequencies, in particular, between the dominant frequency and its first few harmonics.



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