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About Global RTOFS

Summary

The Global RTOFS ocean model is based on an eddy resolving 1/12° global HYCOM (HYbrid Coordinates Ocean Model) (Chassignet et al., 2009) and is part of a larger national backbone capability of ocean modeling at NWS in a strong partnership with US Navy. The Global RTOFS ocean model became operational 25 October 2011.

A Brief Description

A poster on the Global RTOFS ocean model presented at the GODAE OceanView - GSOP - CLIVAR Workshop on Observing System Evaluation and Intercomparisons, Univ. of California Santa Cruz, CA, USA, 13-17 June 2011, is available here.

Based on the successful design of the existing operational Atlantic RTOFS model (Mehra and Rivin, 2010), the global ocean forecast system runs once a day and produces 2-day nowcasts and 6-day forecasts using the daily initialization fields produced at NAVOCEANO using NCODA, a 3D multi-variate data assimilation methodology (Cummings, 2005). The data types assimilated include in situ profiles of temperature and salinity from a variety of sources and remotely sensed SST, SSH and sea-ice concentrations. The operational ocean model configuration has 32 hybrid layers and a horizontal grid size of (4500 x 3298) . The grid has an Arctic bi-polar patch north of 47°N and a Mercator projection south of 47°N through 78.6°S (Figure 1 below). The coastline is fixed at 10 m isobath with open Bering Straits. The potential temperature is referenced to 2000 m depth (sigma-2) and the first level is fixed at 1 m depth. The dynamic ocean model is coupled to a thermodynamic energy loan ice model and uses the KPP mixed layer formulation (Large et al., 1994). The forecast system is forced with 3-hourly momentum, radiation and precipitation fluxes from the operational Global Forecast System (GFS) fields.

Results include daily volume and 3 hourly surface fields in netCDF format with CF conventions. Some surface fields in GRIB format are also generated for internal use at NWS.

Global RTOFS Grid Figure 1: Grid for the global ocean forecast system with each cell representing 54th row and 75th column of the grid. Salinity across P-14 WOCE section Figure 2: Salinity in the Global RTOFS model along the meridional P-14 WOCE section.

Future Plans

In-house analysis and initialization of this system at NCEP using a 3DVAR data assimilation will be developed in time for the next machine (hardware) upgrade expected in 2014. Long term plans also include providing initial and boundary conditions to existing operational regional and coupled hurricane forecast systems at NCEP. A coarser version will also serve as the ocean component of a future climate forecast system.

References

  • Bleck, R., 2002: An oceanic general circulation model framed in hybrid isopycnic-cartesian coordinates. Ocean Modeling, 4, 55-88.

  • Chassignet, E.P., H.E. Hurlburt, E.J. Metzger, O.M. Smedstad, J. Cummings, G.R. Halliwell, R. Bleck, R. Baraille, A.J. Wallcraft, C. Lozano, H.L. Tolman, A. Srinivasan, S. Hankin, P. Cornillon, R. Weisberg, A. Barth, R. He, F. Werner, and J. Wilkin, 2009. U.S. GODAE: Global Ocean Prediction with the HYbrid Coordinate Ocean Model (HYCOM). Oceanography, 22(2), 64-75.

  • Cummings, J.A., 2005: Operational multivariate ocean data assimilation. Quart. J. Royal Met. Soc., Part C, 131(613), 3583-3604.

  • Large, W.C., J.C. McWilliams, and S.C. Doney, 1994: Oceanic vertical mixing: a review and a model with a nonlocal boundary layer paramterization. Rev. Geophys., 32, 363-403.

  • Mehra, A. and I. Rivin, 2010: A Real Time Ocean Forecast System for the North Atlantic Ocean. Terr. Atmos. Ocean. Sci., Vol. 21, No. 1, 211-228.

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Page last modified: Friday, 05-Oct-2012 19:02:29 UTC