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The Global Real-Time Ocean Forecast System (Global RTOFS) 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
In 2020 the Global RTOFS ocean model was upgraded to Version 2.0, which
introduces a high-resolution ocean data assimilation
capability to the forecast system for the first time (Garraffo, et
al., 2020). Global RTOFS
provides predictions for up to eight days of ocean currents, salinity,
temperature and sea ice conditions around the world.
The NOAA announcement regarding the upgraded system is here:
NOAA upgrades flagship ocean forecasting system
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
The Global RTOFS ocean model, based on an earlier operational
Atlantic RTOFS ocean model (Mehra and Rivin. 2010),
runs once a day and produces a nowcast and 8 days of
forecasts. The Global RTOFS model is initialized with RTOFS-DA (based
on 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 41 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 bathymetry minimum depth is 5 m
with open Bering Straits, designed to be compatible with CICE.
The potential temperature is referenced to
2000 m depth (sigma-2) and the first level is fixed at 1 m depth.
The Global RTOFS ocean model is coupled to the
Community Ice CodE (CICE) Version 4.
CICE is a computer code developed
through years of community collaborations, which solve a collection of
mathematical equations that represent the physical processes that
occur during sea ice evolution: growth, melting, and movement of sea
ice, along with the snow and melt water carried with it. CICE is
maintained by the CICE
The forecast system is forced with 3-hourly momentum, radiation and
precipitation fluxes from the operational Global Forecast System (GFS)
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.
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.
Garraffo, Z.D., J.A. Cummings, S. Paturi, Y. Hao, D. Iredell, T.
Spindler, B. Balasubramanian, I. Rivin, H-C. Kim, A. Mehra, 2020.
RTOFS-DA: Real Time Ocean-Sea Ice Coupled Three Dimensional
Variational Global Data Assimilative Ocean Forecast System.
In: Research Activities in Earth System Modelling, edited by E.
Astakhova, WMO, World Climate Research Program Report No.6, July 2020.
(PDF, available here)
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,