Nonlinear vertical mixing processes in the ocean: modeling and parameterization

Abstract

Nonlinear vertical mixing processes are critical in the transport of heat and momentum throughout the ocean and are especially important in the surface mixed layer and in deep convection. This paper reviews recent numerical modeling studies that are being used to help develop more effective parameterizations of nonlinear vertical mixing processes. In particular, we describe two oceanic process studies using a large-eddy simulation (LES) turbulence model and review the performance of an improved vertical mixing parameterization in an ocean general circulation model. The first process study examines the role of wind and heat-flux forcing of turbulence in the tropical western Pacific ocean surface mixed layer. Results from the LES show that mixing is dominated by three key processes: Langmuir circulation near the surface, organized circulations that extend through the mixed-layer depth, and shear instability at the mixed-layer base. The second LES study centers on the onset and strength of deep oceanic convection. Results from this study show that the growth of convective plumes is dependent on the integral properties of heat and salinity forcing. The paper concludes with a test of an improved parameterization of deep convection for ocean general circulation models.