Langmuir circulation and its relation to surface forcing during CBLAST

As a part of the 2003 Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Low-Wind Experiment, instrumentation was deployed at the Air-Sea Interaction Tower (ASIT) about 2 miles south of Martha's Vineyard, Massachusetts. Sensors on the ASIT, a fixed structure spanning the water column (15 m depth) and the lower 20 m of the atmosphere, provided surface forcing data along with oceanic stratification and currents. These data were used to determine parameters relevant to the generation and scale of Langmuir circulation, such as friction velocity u*, Stokes drift velocity Us, the turbulent Langmuir number La = sqrt(u*/Us) and the mixed layer depth. The observed strength and dominant scale of Langmuir circulation were determined from a surface-scanning acoustic Doppler current profiler (ADCP) that measured the horizontal structure of velocity near the ocean surface at scales from ~10-100 m. The relationship between observed Langmuir circulation strength and surface forcing is explored, with particular attention to the range of La within which circulation is observed, the scaling of circulation strength with (u*Us), and the influence of wave age Cp/u* on circulation strength.