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 wave s can disintegrate an oil film, generating oil droplets or blobs of mater-i n-oil emulsions when the oil is weathered. Langmuir circulation, with its c onvergent and divergent flow at the ocean surface, can organize the floatin g particles into nearly parallel bands aligned in the wind direction. Howev er, the rapid temporal evolution of the circulation makes it an effective m echanism for dispersing particles. In this paper, we estimate horizontal di ffusivities of floating particles by examining Lagrangian particle statisti cs inferred from sonar images of the ocean surface. The diffusivities are i n the range of O(10(-3))-O(1) m(2) s(-1) and depend on the crosswind and do wnwind velocities in Langmuir circulation. The particle dispersion on the o cean surface is not isotropic. The diffusivity in the crosswind direction i s generally larger than that in the downwind direction. (C) 2001 Elsevier S cience Ltd. Ah rights reserved.