Large Scale Oceanic Drogue Diffusion

Abstract

OCEANIC turbulent diffusion is not well understood. Dye diffusion techniques are usually used to estimate diffusivity, but Lagrangian (particle) techniques are also useful, especially on a large scale. The most successful empirical method of organizing measurements of diffusing particles stems from Richardson's neighbour-diffusion theory¹. Briefly, the probability q(l, t) of two particles being a distance l apart is governed by the equation where F(l) is the neighbour diffusivity and t is time. It follows² that F is given by where l₀ is the initial separation, Δl is the change in separation in time Δt, and the bar indicates an average over a class interval of value l₀ + 0.5 Δl. Data are relatively plentiful for l<100 m, but sparse for greater values of l (ref. 3). The data available indicate a power law where n≈4/3, and k ranges (for different experiments) from 0.005 to 0.073 cm^2/3 s⁻¹.