Estimating horizontal dispersion of floating particles in wind-driven upper ocean

Breaking waves and Langmuir circulation are dominant turbulent processes in a mind-driven upper ocean. Surface waves and, in particular, breaking waves can disintegrate an oil film, generating oil droplets or blobs of mater-in-oil emulsions when the oil is weathered. Langmuir circulation, with its convergent and divergent flow at the ocean surface, can organize the floating particles into nearly parallel bands aligned in the wind direction. However, the rapid temporal evolution of the circulation makes it an effective mechanism for dispersing particles. In this paper, we estimate horizontal diffusivities of floating particles by examining Lagrangian particle statistics inferred from sonar images of the ocean surface. The diffusivities are in the range of O(10(-3))-O(1) m(2) s(-1) and depend on the crosswind and downwind velocities in Langmuir circulation. The particle dispersion on the ocean surface is not isotropic. The diffusivity in the crosswind direction is generally larger than that in the downwind direction. (C) 2001 Elsevier Science Ltd. Ah rights reserved.