A SIMILARITY ANALYSIS OF THE STRUCTURE OF AIR-FLOW OVER SURFACE-WAVES

Previous field investigations of the wave-induced pressure field have focused on determination of the momentum input from wind to the surfac e waves. This is useful for the estimation of wave growth rate and, in particular, the wave growth parameter p. Due to the difficult nature of experimental study of airflow very close to the wave surface, it ha s been necessary to extrapolate elevated measurements of the wave-indu ced pressure field to the surface. This practice may be incorrect with out adequate knowledge of the complex vertical structure of the pressu re field. In addition, the wave-induced pressure and velocity fields a re coupled to the near-surface turbulence. Hence, understanding the na ture of the wave-induced how fields is critical for modeling of the ne arsurface wind and wave fields. Utilizing a simple similarity hypothes is, detailed vertical structure of the wave-induced pressure and veloc ity components is examined. Results of this analysis are presented usi ng data obtained in the spring and fall of 1994 during the Riso Air-Se a Experiment program. These results demonstrate that, when compared to theory, simple extrapolation of measurements of the wave-induced pres sure field from a fixed height above the surface may contribute to the uncertainty of measured growth rates. In addition, it is demonstrated that an analogous similarity relationship for the wave-induced vertic al velocity field yields results that are consistent with previous lab oratory studies.