Observations on the Directional Development of Wind-Waves in Mixed Seas
Abstract
Sea surface measurements recorded by a Directional Waverider buoy, deployed in the Gulf of Mexico, served as the basis of this investigation into the evolution of wind waves in mixed seas. Five events of mixed seas were selected and examined in detail. These events chronicled the growth of new wind seas in the presence of background swell during periods of high wind forcing. Under sufficiently high wind forcing, the wind sea system developed similarly to cases of pure wind waves. Wind wave systems under wind action were found to grow at an angle to the wind vector and away from the mean direction of the low frequency wave system. Under low winds, the wind sea evolution was dominated by interactions with swell. Situations of mixed seas showed that coupling between wave systems had a stabilizing effect of reducing a multimodal energy spectrum to a unimodal wave spectrum. Coupling between wave systems was observed to occur over local frequencies as predicted by the weakly nonlinear wave wave interaction theory, and also over a wider frequency range. In cases where the energy spectrum of swell and wind sea was distinctly bimodal, an equivalent wind sea was partitioned from the long wave components to allow for a comparison with the growth of pure wind waves. The directionality of the wind sea and swell systems was found to influence the development of wind waves. The directional spread distribution of mixed seas exhibited features different from those of pure wind seas. The minimum angular spread of wind seas was generally located at or above the wind wave peak frequency. Finally, this modest collection of data supported the current hypothesis that opposed swell intensifies wind wave growth, whereas an aligned swell attenuates wave growth.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1998
- Accession Number
- ADA345542
Entities
People
- Dung Nguy
Organizations
- University of Washington