Relative particle motion in capillary waves

When a container of fluid is oscillated vertically, capillary waves develop on the surface if the amplitude exceeds a critical value. Experimentally one finds that the motion of small particles on the surface of the fluid is close to Brownian. Here we study the relative motion of particle pairs. The experiment establishes that particle motion is strongly correlated over macroscopic distances. Our observations are in striking agreement with upper-ocean studies, and with theories that appear applicable to this ''weak turbulence'' problem, and in disagreement with experimental and theoretical results for two-dimensional large-scale atmospheric turbulence.