Parametrisation of the Ocean Surface Boundary Layer: The OSMOSIS scheme
The new OSMOSIS parameterisation scheme for the OSBL is a response to this challenge. The scheme determines the depth of the OSBL using a new prognostic equation and then uses non-local flux-gradient relationships to parametrize turbulent transports within the OSBL. The flux-gradient relationships, are based on approximations to the turbulence flux budgets. Data from large eddy simulations is used to motivate and calibrate the scheme. Wave driven Langmuir turbulence is represented and the scheme, and is sufficiently flexible to accommodate representation of restratification by submesoscale circulations.
Comparisons with observations taken during the OSMOSIS project show early promise. The scheme represents well the diurnal variation of the OSBL during light wind conditions, the deepening of the OSBL during winter, and the restratification during spring. The basic scheme indicates significant over-deepening during winter, which signals new physics. Early indications are that submesoscale motions are playing a strong role at this time, and representing them substantially improves the results.
The scheme is currently being implemented and tested in Nucleus for European Modelling of the Ocean (NEMO).