Evolution of ocean slicks under a rising wind

Abstract

Airborne synthetic aperture radar and high‐resolution infrared imagery are used to examine the evolution of natural ocean slicks during a period of freshening wind. Initially the slicks are of the order of 50 m in width and have radar and thermal contrasts of the order of 10 dB and several 0.1°C. While there can be over time a transient reorganization of surface film material by internal waves, the slicks are observed to disperse and are no longer detectible after 5 h. The dispersion occurs through the action of Langmuir circulation, which results in along‐wind streaks or “windrows”, as well as other effects. Prominent streaks occur preferentially along a slick's upwind side, the downwind side resembling more of a “leading edge”, at least early on. Over time, the leading edge develops a corrugated shape, and gaps begin to develop within the slicks. The formation of gaps is compared with a conceptual model by Dysthe (2006) for the tearing of a surface film in the region of positive surface straining. Eventually, the slicks break into elongated patches that co‐exist with windrows, which is consistent with the effects of advective dispersion.