Model Description
The ocean model is the Naval Research Laboratory (NRL) Layered Ocean Model
(NLOM). It is a nonlinear, free surface, primitive equation model that was originally
developed by Hurlburt and Thompson (1980) for the Gulf of Mexico. Fratantoni
et al. (1995, 2000) used an Atlantic Ocean configuration of NLOM in their
studies of NBC rings and other mass transport pathways in the tropical
Atlantic. Here the 1/16° global, seven layer, thermodynamic version of NLOM is employed
with assimilation of sea surface height (SSH) and sea surface temperature (SST)
data.
The SSH data are the TOPEX/POSEIDON and ERS-2 satellite altimeter data. This model is the foundation of the global ocean
nowcast/forecast system developed at NRL and running in real time at the Naval
Oceanographic Office since October 2000. For this study, a reanalysis of the
remotely-sensed data was performed beginning in January 1993, shortly after the
TOPEX/POSEIDON altimeter data became available. In addition to producing a
time series going nearly as far back as the beginning of continuously available
satellite altimeter data, the reanalysis takes advantage of improved satellite orbit
corrections that occur after operational model run time.
The model is forced at the surface by wind stresses and heat fluxes from the Navy
Operational Global Atmospheric Prediction System (NOGAPS) (Hogan and Rosmond,
1991). The global thermohaline circulation is included in the model via
observationally-based (Mauritzen, 1993) mass fluxes imposed at the northern boundary in the Atlantic Ocean.
The amplitude of the MOC
is consistent with
Schmitz and McCartney (1993). The non-data-assimilative version of the model
realistically simulates the major gyres, fronts and eddies (including NBC
rings). This is essential in order for the model to perform skillfully as
a dynamical interpolator of satellite altimeter data and as a forecast model.
For the model equations and additional details about NLOM, see Wallcraft
(1991), Hurlburt et al. (1996), Shriver and Hurlburt (1997), Wallcraft and
Moore (1997), and Moore and Wallcraft (1998). Smedstad and Fox (1994) provide
information on the altimeter data assimilation and Kara et al. (2001) describes
the mixed layer model and SST in NLOM.
Nowcasts and forecasts from the NLOM-based real time system as well as forecast
skill assessments for many regions of the global ocean (including the NBC
region) can be viewed on the world wide web at
http://www7320.nrlssc.navy.mil/global_nlom/.
The ocean model is the Naval Research Laboratory (NRL) Layered Ocean Model
(NLOM). It is a nonlinear, free surface, primitive equation model that was originally
developed by Hurlburt and Thompson (1980) for the Gulf of Mexico. Fratantoni
et al. (1995, 2000) used an Atlantic Ocean configuration of NLOM in their
studies of NBC rings and other mass transport pathways in the tropical
Atlantic. Here the 1/16° global, seven layer, thermodynamic version of NLOM is employed
with assimilation of sea surface height (SSH) and sea surface temperature (SST)
data.
The SSH data are the TOPEX/POSEIDON and ERS-2 satellite altimeter data. This model is the foundation of the global ocean
nowcast/forecast system developed at NRL and running in real time at the Naval
Oceanographic Office since October 2000. For this study, a reanalysis of the
remotely-sensed data was performed beginning in January 1993, shortly after the
TOPEX/POSEIDON altimeter data became available. In addition to producing a
time series going nearly as far back as the beginning of continuously available
satellite altimeter data, the reanalysis takes advantage of improved satellite orbit
corrections that occur after operational model run time.