Large-Eddy Simulation of Pressure Transport Below the Mixed Layer

Deep convection energizes the entire water column. Large-eddy simulation of the oceanic boundary layer system predicts turbulence in the well-mixed layer as well as turbulence-induced internal waves propagating into the underlying stratified water column of the freely convecting wintertime Labrador Sea. Of particular interest is the downward propagation of energy from the turbulent boundary layer by pressure transport and the buildup of internal wave energy in response to local atmospheric forcing. A near equilibrium internal wave spectrum is approached after about two weeks of episodic storm cooling. A broad band omnidirectional internal wave field with peak energy near the buoyancy frequency N is forced mostly by the surface buoyancy flux. The pressure transport of mixed-layer kinetic energy carries about 30 % of the available energy into the stratified zone and causing entrainment. On average, 10 W/m or about 1% of the winter Labrador Sea mixed-layer energy escapes into the pycnocline where it is converted into internal wave energy.