Direct Measurement of Turbulent Diffusion Induced by Waves in a Tank

Turbulent diffusivity D is estimated in laboratory experiments in a wind-wave tank. The estimates make an initial verification of the available theoretical results on the dependence of D on different parameters possible. To estimate D by the Einstein formula, we use measurements of the spreading rate of an inkblot in a water layer under waves. A comparison between the estimates and a set of model parameterizations of D has shown the statistical advantage of parameterization D proportional to u(*)a(0)delta in the presence of wind waves and parameterization D proportional to a(0)(3)f(p)/z in the presence of mechanical waves (u(*) is the friction velocity, a(0) is the wave amplitude on the surface, f(p) is the wave-spectrum peak frequency, delta is wave steepness, and z is the measuring depth). The measurement procedure and the technique for comparison between the theory and experiment are discussed.