Observations and numerical simulations of large-eddy circulation in the ocean surface mixed layer
2014-11-06,
Sundermeyer, Miles A.,
Skyllingstad, Eric D.,
Ledwell, James R.,
Concannon, Brian,
Terray, Eugene A.,
Birch, Daniel,
Pierce, Stephen D.,
Cervantes, Brandy T. Kuebel
Two near-surface dye releases were mapped on scales of minutes to hours temporally, meters to order 1 km horizontally, and 1–20 m vertically using a scanning, depth-resolving airborne lidar. In both cases, dye evolved into a series of rolls with their major axes approximately aligned with the wind and/or near-surface current. In both cases, roll spacing was also of order 5–10 times the mixed layer depth, considerably larger than the 1–2 aspect ratio expected for Langmuir cells. Numerical large-eddy simulations under similar forcing showed similar features, even without Stokes drift forcing. In one case, inertial shear driven by light winds induced large aspect ratio large-eddy circulation. In the second, a preexisting lateral mixed layer density gradient provided the dominant forcing. In both cases, the growth of the large-eddy structures and the strength of the resulting dispersion were highly dependent on the type of forcing.