About Global RTOFS
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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.
Figure 1: Grid for the global ocean forecast system with each cell
representing 54th row and 75th column of the grid.
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
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Bleck, R., 2002: An oceanic general circulation model framed in hybrid
isopycnic-cartesian coordinates. Ocean Modeling, 4, 55-88.
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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.
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Cummings, J.A., 2005: Operational multivariate ocean data assimilation.
Quart. J. Royal Met. Soc., Part C, 131(613), 3583-3604.
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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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