AUV observations of Langmuir turbulence in a stratified shelf sea

Measurements collected by a REMUS 600 AUV off the coast of southern
California demonstrate large-scale coherent wave-driven vortices,
consistent with Langmuir turbulence (LT), played a dominant role in
structuring turbulent dissipation within the oceanic surface boundary
layer. During a 10-hour period with sustained wind speeds of 10 m/s,
Langmuir circulations were limited to the upper third of the surface mixed
layer by persistent stratification within the water column. The
ensemble-averaged circulation, calculated using conditional averaging of
AD2CP velocity profiles using elevated backscattering intensity associated
with subsurface bubble clouds, indicates that LT vortex pairs were
characterized by an energetic downwelling zone flanked by broader, weaker
upwelling regions with vertical velocity magnitudes similar to previous
numerical studies of LT. Horizontally-distributed microstructure estimates
of turbulent kinetic energy dissipation rates were lognormally-distributed
near the surface in the wave mixing layer with the majority of values
falling between wall layer scaling and wave transport layer scaling.
Partitioning dissipation rates between downwelling centers and ambient
conditions suggests that LT may play a dominant role in elevating
dissipation rates in the OSBL by redistributing wave-breaking turbulence.