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HYCOM parameter sensitivities under CORE forcing
Rainer Bleck
NASA Goddard Institute for Space Studies, Columbia Univ., New York
(Abstract received 07/20/2007 for session X)
ABSTRACT
A series of multi-century experiments with a 2 degree, 20-layer version of HYCOM subjected to CORE (Coordinated Ocean-Ice Reference Experiments) \"normal year\" forcing have been carried out to investigate the sensitivity of the modeled circulation to various parameter choices. Parameterizations whose impact has been studied include (a) formulation of bulk air-sea fluxes (Large & Yeager versus Kara); (b) treatment of salinity transients resulting from E-P imbalances; (c) choice of reference profile in the treatment of thermobaricity; (d) constants affecting ice growth in the Parkinson-Washington ice model used; (e) diapycnal diffusivity and bolus flux coefficients; (f) surface salinity restoration. One of the principal shortcomings of CORE-type boundary forcing is the lack of feedback between SST and atmospheric humidity. This can cause serious errors in evaporative flux calculations, leading to E-P imbalances whose removal strategy becomes a matter of choice. In the present round of experiments, the most realistic thermohaline circulation was obtained by confining corrective moisture fluxes to the Southern Ocean and omitting surface salinity relaxation so as not to interfere with the buildup of a strong southern seasonal halocline. Rigorous adherence to the OCMIP protocol leads to a substantial weakening of the Atlantic overturning circulation.
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2007 LOM Workshop, Bergen, Norway, August 20-22, 2007