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Surface fluxes and Ocean state estimates in the eastern |
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Subtropical North Atlantic. |
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Olwijn Leeuwenburgh, Patrick Heimbach and Detlef Stammer |
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A coarse resolution regional ocean model of the eastern |
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subtropical North Atlantic is used in a 5-year run to |
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investigate the effects of two different surface forcing |
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formulations and of several strategies to minimize a cost |
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function in the context of ocean state estimation. |
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The model is a 2 degree resolution application of the |
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MITgcm which is forced at the open boundaries by |
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temperature, salinity and current velocities obtained |
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from a global implementation of the same OGCM. The assimilated |
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data consist of T/P and ERS altimetry, a mean sea surface |
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estimate, and Reynolds SST, and the results are compared |
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with independent buoy data obtained from the Subduction |
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Experiment. Different strategies to bring the model |
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into consistency with ocean observations are being discussed. |
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All of them use the models adjoint to adjust control variables, |
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such as the initial state, lateral boundary conditions and surface |
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forcing. Control terms include either the surface fluxes of momentum, |
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net heat and freshwater fluxes, or the atmospheric state as control |
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variables. Early results indicate that there are distinct differences |
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in magnitude and behavior of the cost function depending on |
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the type of forcing and the manner in which control |
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variables are included and adjusted. While a bulk-formulae |
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type forcing leads to better initial agreement between |
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model and data, the optimization is more effective (faster |
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decay) with the traditional type of flux forcing. |
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