The Arrested Ekman Layer Escapes! Ventilation of the BBL by Internal Swash.

Moored data from the northern Deepwater Gulf of Mexico in the vicinity of DeepWater Horizon are presented.  Subinertial flows of O(0.1-0.2 m/s) are in the sense of Kelvin wave propagation and support a downwelling Ekman layer with reduced near boundary stratification.  The moored data document cross-slope and vertical buoyancy fluxes dominated by a frequency band that includes diurnal and inertial frequencies and extend to about an order of magnitude larger than inertial.  We refer to this frequency band as internal swash and the region of reduced stratification at the bottom boundary exhibiting these fluxes as the internal swash zone.  Vertical fluxes of cross-slope momentum associated with internal swash band frequencies are large, of similar order of magnitude as the drag associated with the viscous no-flow bottom boundary condition on the cross-slope subcentral current.  Typical mixing efficiencies of (Γ ~ 0.2) are found in association with elevated mixing O(100 times background) one-to-two hundred meters above the bottom. This enhanced turbulence appears in conjunction with near-inertial frequency motions that may be dynamically coupled to the mean flow.