Ambient and breaking roughness of the ocean surface

Local wind-generated surface roughness can be decomposed into ambient component, surface wave geometric contribution (the mean square slope) and breaking wave contribution (the breaking roughness). Only the last two components can be attributed to local wind condition for remote sensing considerations. The ambient roughness level is estimated to be between 0.01 and 0.02 from altimeter data. The rate of increase of breaking roughness with wind speed is much faster than the counterpart of the mean square slope of wave geometry. In high wind conditions, breaking roughness contribution may exceed the wind-wave geometrical contribution. The data of Cox and Munk (1954) collected in clean and slick conditions, and newer data of filtered surface roughness derived from spaceborne altimeter are analyzed to provide a quantitative description of the breaking roughness.