Suppression of capillary waves by surface-active films

Minute amounts of ampiphillic molecules at an air-water interface can have striking effects on both the damping and generation of capillary waves. The theory of these effects within linearized hydrodynamics is reviewed. The conventional wisdom is that oil calms troubled waters by increasing the rate of capillary wave damping. Although surface-active films can increase the damping rate by factors of two to four, a potentially more important effect is the suppression of capillary wave generation by the wind. In particular, generation by the components of fluctuating Reynold's stresses in the atmosphere parallel to the surface can be reduced by an order of magnitude or more. The theory predicts a more modest suppression of the effect of Reynold's stresses normal to the surface.