Validation, Verification, and Exploitation of an Ocean Model for Decision Support

New ocean models at ever higher resolutions are being developed for use in specific naval operational areas and operational decision processes. There is an urgent need for validation and verification of these new models and their products as they are being brought on line over the next 1-2 years. A full understanding of the uncertainties—the variability of the ocean environment, and the predictive system’s ability to portray that variability—is needed to make operational decisions that hinge on these predictions. We examine the validity and uncertainty in the Navy Coastal Ocean Model (NCOM; Barron et al 2006) for the area of the Western Atlantic. NCOM is a hybrid s/z level model based on primitive equations. In the global configuration used for operational needs, while there are 41 s-z level surfaces, the fields used for analyses have been gridded to a standard set of 40 z-level surfaces. These are the fields available to operational users. The global operational model is run at a horizontal resolution of approximately 1/8°. The analysis we present here is based on the output that has been re-gridded to a uniform grid of 1/8° in resolution. The model is forced by wind stress, air temperature, air mixing ratio, and net solar radiation provided by Fleet Numerical Meteorology and Oceanography Center (FNMOC)’s Navy Operational Global Atmospheric Prediction System every three hours. The model fields that are analyzed in this paper are from sequential 48 hour forecast runs of the system. That is, each day, using an initial field created from previous a previous model state and observed data, the simulation is run for 48 hours into the future using the forecast atmospheric fields from the NOGAPS. Each 24 hours, the model system includes an analysis step to “reset” the initial state of the ocean at the beginning of the next 48-hour forecast. Our comparison of the initial field of a 2-day forecast run to the field 48 hours later shows close similarity in the strong features of the Gulf Stream. Thus, most of the discrepancy between observations and the model simulation is in the bias associated with the initial field rather than the changes that occur due to model dynamics over 48 hours. Given this understanding, this paper concentrates on the changes that occur over 48 hours and how to understand the uncertainty associated with metrics such as frontal location and mixed layer depth in terms of predictability and the local dynamics of the system. Barron, C.N., A.B. Kara, P.J. Martin, R.C. Rhodes, and L.F. Smedstad, 2006: Formulation, implementation and examination of vertical coordinate choices in the global Navy Coastal Ocean Model (NCOM). Ocean Modelling, 11(3-4), 347-375, doi:10.1016/j.ocemod.2005.01.004.