Compressible flow: Turbulence at the surface

In a study of compressible flow, we have tracked the motion of particles that float on a turbulent body of water. The second moment of longitudinal velocity differences scales as in incompressible flow. However the separation [R-2(t)] of particle pairs does not vary in time according to the Richardson - Kolmogorov prediction [R-2(t)] proportional to t(3). As expected, the self diffusion [d(2)(t)] shows a crossover between ballistic motion [d(2)(t)] proportional to t(2) at small t and uncorrelated motion [d(2)(t)] proportional to t in the longtime limit.