Abstract
The Navy Coastal Ocean Model Four-Dimensional Variational Assimilation (NCOM 4DVAR ) system is an analysis software package that is designed to supplement the current capability of the operational analysis/prediction system known as the Relocatable Navy Coupled Ocean Model (Relo NCOM ) system. The present assimilation component of Relo NCOM employs the Navy Coupled Ocean Data Assimilation Three-Dimensional Variational Assimilation (NCODA 3DVAR) system to process and assimilate observations. The NCOM 4DVAR, on the other hand, uses a representer based 4DVAR method and has been found to improve the forecast-skill for several regional applications. This chapter presents the results of validation experiments performed in the Okinawa Trough. The analysis and resulting forecast skill of the two assimilation methods within Relo NCOM (NCOM 4DVAR and NCODA 3DVAR ) are compared, and the operational implementation of NCOM 4DVAR is examined to verify that it satisfies operational constraints. The metrics used to validate the NCOM 4DVAR system include: computational efficiency, scalability, robustness, and the prediction accuracy of temperature, sea surface height, and sonic layer depth through NCOM 4DVAR and NCODA 3DVAR analyses. Forecast skill metrics are computed using surface observations of temperature, salinity and sea surface height, and profile observations from gliders and AXBTs (aerial expendable bathythermograph). Overall, the validation reveals that NCOM 4DVAR has lower root mean square errors for both analyses and forecasts than the operational NCODA 3DVAR system.
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Acknowledgements
The authors were supported by the NRL 6.4 NCOM 4DVAR Rapid Transition Project (projects 4727-04 and 4727-14), which was managed by both Space and Naval Warfare Systems Command under program element 063207N and the Office of Naval Research under program element 0602435N. Numerical simulations were performed at the DoD Supercomputing Resource Center (DSRC) with grants of computer time from the HPCMP Variational Assimilation High Performance Computing (HPC) subproject.
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Smith, S., Ngodock, H., Carrier, M., Shriver, J., Muscarella, P., Souopgui, I. (2017). Validation and Operational Implementation of the Navy Coastal Ocean Model Four Dimensional Variational Data Assimilation System (NCOM 4DVAR) in the Okinawa Trough. In: Park, S., Xu, L. (eds) Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications (Vol. III). Springer, Cham. https://doi.org/10.1007/978-3-319-43415-5_18
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