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An Integrated Energetics Approach to Determining Planetary Boundary Layer Mixing
Robert Hallberg
NOAA/GFDL
(Abstract received 04/30/2015 for session X)
ABSTRACT
The ocean’s surface boundary layer is critical for modeling the climate system, and the design of the surface boundary layer can have a profound effect on the overall stability of the coupled system. Prompted by high-latitude coupled numerical instabilities that arise when using the K-profile parameterization (KPP) with a high vertical and horizontal resolution configuration of MOM6, GFDL is reconsidering its approach to modeling the surface mixed layer. The most sophisticated approaches to ocean turbulence modeling use two equation closures, with one equation for the turbulent kinetic energy (TKE) and another for the dissipation rate, turbulence length scale or the diffusivity itself, but are typically too complicated to step these equations implicitly along with their impacts on the ocean state. By contrast KPP solves a relatively simple equation for the diffusivity profile based on the depth at which a bulk Richardson number first attains a critical value, but lacks an explicit TKE conservation equation. Traditional bulk mixed layer models solve a TKE and potential energy balance equation implicitly for the consequences of mixing, which is made mathematically simply by assuming that the water is perfectly homogenized (and diffusivities are extremely large) within the surface mixed layer. This talk will present a new approach to modeling mixing in the ocean’s surface boundary layer, based on an integrated implicit energy balance equation (similar to a bulk mixed layer) but with finite diffusivities (similar to KPP or a two-equation closure). The mathematical tractability and greater numerical stability of this integrated energetics approach to modeling the ocean’s surface boundary layer make it a very promising approach for use in coupled climate modeling.
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2015 LOM Workshop, Copenhagen, Denmark June 2nd - 4th, 2015