Cold Filament Frontogenesis and Arrest by Ocean Boundary Layer Turbulence
Abstract
The spatial and temporal state of the upper ocean boundary layeris determined by a set of poorly understood complex interactionsbetween submesoscale turbulence, (e.g., fronts, dense filaments andcoherent vortices) and small-scale boundary-layer turbulence. Ofparticular interest here is the life-cycle of a cold dense filamentundergoing frontogenesis in the presence of wind-wave generatedLangmuir turbulence. Cold filaments generate secondary circulationsthat are frontogenetic with super-exponential sharpening of thecross-filament buoyancy and horizontal velocity gradients. Withinless than a day, the frontogenesis is arrested at a very smallwidth, < 100 m, primarily by boundary layer turbulence, with asubsequent slow decay by further turbulent mixing. This phenomenonis examined in Large-Eddy Simulations (LESs) with resolved turbulentmotions in large-horizontal domains using 10^9 gridpoints. Windsand waves are oriented in directions both perpendicular and parallelto the cold filaments in the LES. The LES solutions show that theboundary layer turbulence is strikingly inhomogeneous in relationto the submesoscale filamentary currents and density stratification,and there is large horizontal transport of cold water at the baseof the mixed layer. Also, the spatial and temporal evolution offrontogenesis is dependent on the orientation of the winds andwaves, and for some wind-wave combinations the sharp filamentexhibits an unexpected submesoscale lateral shear instability thatfacilitates the frontogenetic arrest.
- Publication:
-
American Geophysical Union, Ocean Sciences Meeting
- Pub Date:
- February 2016
- Bibcode:
- 2016AGUOS.A53A..06S
- Keywords:
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- 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICALDE: 4520 Eddies and mesoscale processes;
- OCEANOGRAPHY: PHYSICALDE: 4568 Turbulence;
- diffusion;
- and mixing processes;
- OCEANOGRAPHY: PHYSICALDE: 4572 Upper ocean and mixed layer processes;
- OCEANOGRAPHY: PHYSICAL