Observed Growth of Langmuir Circulation

Surface velocity patterns and upper ocean density profiles are presented from a period following a sudden increase in wind. A prior wind speed of 8 m/s failed to produce visible signs of Langmuir circulation. After the wind speed increased to 13 m/s, Langmuir circulation developed within 15 min. The initial scale observed was about 16 m, streak to streak, and may have been restricted by the depth scale of the measurements. This spacing is about two thirds of the dominant wavelength (4-s-period waves). The streak spacing (two cell widths) increased at roughly 40 m/h for the next hour. The density measurements indicate a depth of mixing which increased over the same period at a rate of 20 m/h; thus the vertical to horizontal aspect ratio was about 1:1. Prior stratification was weak (buoyancy frequency of about 1.5 cph), and probably did not affect the circulation initially.