Surface fluxes for practitioners of global ocean data assimilation

The ability of available ocean surface fluxes to meet the demands of the Global Ocean Data Assimilation Experiment (GODAE) for global, near real time, fields of known uncertainty is examined. Surface flux problems that are discussed in detail include the lack of direct surface measurements to serve as a standard, the difference between fluxes measured at height above the sea and the desired surface fluxes, the complications posed by the need for ocean-ice fluxes, and the large number of global fields required to describe the fluxes. The formulation of the air-sea, ocean-ice and air-ice fluxes of momentum, heat and freshwater, in terms of these fields is detailed from the measurements (including satellite based flux estimates) to the parameterizations. Air-ice fluxes are included to cover the possibility of coupling a sea-ice model within the data assimilation system. The position that there is no one set of flux products that represents the best possible choice for GODAE in all regions and all components is adopted. An alternative merger of a variety of different datasets is described along with objective corrections based on regional and/or short term observations, and ocean model behavior. A flux climatology based on these datasets and observed sea surface temperature is presented as the mean and variability from the seasonal to inter-annual, that GODA flux products should strive to reproduce. The necessary condition of near zero net global heat and freshwater climatological fluxes is demonstrated.

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