Kinematics under wind waves

Abstract

The ocean near surface kinematics were measured as part of the SAXON experiment during the period from 5 to 14 October 1988. A growing wave field due to a passing front with winds up to 17 ms'^ occurred during the first 5 days. A wide range of wind forcing and wave conditions occured during the measurement period. Two orthogonal components of the horizontal velocity were measured using an electromagnetic current meter. The wave directional field was measured using a high resolution 2 meter square slope array. The classical Longuet-Higgins et al (1963) method of computing directional wave spectra and the new exact Fourier coefficients representation method (Grauzinis, 1989) are used to compute directional wave spectra. The new method of computing directional wave spectra, which represents bi-modal distributions of wave energy exactly matching the measured Fourier coefficients to second order, demonstrated improved performance over the classical technique. Phase functions between the sea surface elevation and horizontal velocity components compared well with the results predicted by Unear wave theory. The coherence function of the horizontal velocity components and the sea surface elevation confirmed the dependence on the wave field directivity. Spectra of the sea surface elevation computed from pressure and horizontal velocity data compared well using linear theory transfer functions.