Directional Distributions and Mean Square Slopes in the Equilibrium and Saturation Ranges of the Wave Spectrum

Abstract

Abstract Field observations show that the crosswind component constitutes a significant portion of the ocean surface mean square slope. The average ratio between the crosswind and upwind mean square slope components is 0.88 in slick-covered ocean surfaces. This large crosswind slope component cannot be explained satisfactorily based on our present models of a unimodal directional distribution function of ocean waves. Two-dimensional spectral analysis of the 3D ocean surface topography reveals that a bimodal directional distribution is a common feature for wave components shorter than the peak wavelength. The calculated result of the upwind and crosswind mean square slope components using a bimodal directional distributions yields substantial improvement in agreement with field measurements. Also discussed in this paper is the transition of the spectral function from an equilibrium form to a saturation form. Through comparison with the mean square slope data of the slick cases under which short waves are s...