NOGAPS (Navy Operational Global Atmospheric Prediction System)
The NOGAPS (Navy Operational Global Atmospheric Prediction System) forecast
model is a global model that is spectral in the horizontal and energy-conserving
finite difference (sigma coordinate) in the vertical. The model top pressure
is set at 1 hPa; however, the first velocity and temperature level is approximately
5 hPa. The variables used in dynamic formulations are vorticity and divergence,
virtual potential temperature, specific humidity, and terrain pressure.
On 24 June 1998, NOGAPS was upgraded to version 4.0. The
primary change was an increase in the number of vertical levels from 18
The operational T159L24 NOGAPS (4.0) runs on a CRAY C90 and executes
several times each 00-UTC and 12-UTC watch, including a six-day forecast
completing approximately five and one-half hours past the synoptic time.
NOGAPS currently outputs close to 25,000 gridded fields per day. Products
from NOGAPS are distributed to a worldwide customer base. NOGAPS also provides
essential and tailored input to many other models, including the Navy's
advanced Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS),
ocean wave model, sea ice model, ocean circulation model, ocean thermodynamics
model, tropical cyclone model, aircraft and ship-routing programs, and
application programs at both FNMOC (U.S. Navy's Fleet Numerical Meteorology
and Oceanography Center) and the Air Force Weather Agency (AFWA).
Along with the GFDL tropical cyclone forecast model and
the UK Met Office and Japanese global models, NOGAPS is a primary tropical
cyclone forecast tool for forecasters at the Joint Typhoon Warning Center
(JTWC) and the National Hurricane Center (NHC).
NOGAPS uses a multi-variate optimal interpolation (MVOI) scheme. This
analysis scheme uses multivariate statistical analytical techniques, patterned
after the volume method developed by Lorenc (1981) for ECMWF. First implemented
operationally at FNMOC in January 1988, NOGAPS has undergone evolution
to reach its current configuration. The analysis is performed on the Gaussian
grid of the T159L24 global spectral model on the 16 standard pressure levels
from 1000 to 10 hPa, inclusive. The maximum number of observations used
per volume is 600.
In addition to conventional observations (surface, rawinsonde, pibal,
and aircraft), the analysis makes heavy use of various forms of satellite-derived
observations. The analysis uses derived soundings from the NOAA and DMSP
polar-orbiting satellites as well as DMSP SSM/I total column precipitable
water and surface wind speeds. NOGAPS was the first operational model to
use SSM/I wind speeds (Goerss and Phoebus 1992). In addition to the wind observations
derived from various operational processing centers for the geostationary satellites, the NOGAPS also untilizes high-density multispectral wind observations produced
by the University of Wisconsin-Cooperative Institute for Meteorological
Satellite Studies (CIMSS).
The NOGAPS model time step begins as 540 seconds, but is
dynamically reduced to a shorter time step if stratospheric jets go beyond
a designated threshold.
The physics package includes
-Bulk-Richardson number-dependent vertical mixing patterned after ECMWF's vertical mixing parameterization
-A time-implicit Louis surface
-Gravity wave drag
-Shallow cumulus mixing
of moisture, temperature, and winds
-Convective and stratiform
-Harshvardhan solar and
of gravity wave propagation and Robert time filtering