Global Forecast System
HIGHLIGHTS
- Medium and long-range forecasts by the global version of
the GEM (Global Environmental Multiscale) model
- uniform lat-lon grid with 0.9 degree resolution - 28
eta vertical levels
- 72 h forecast (12 UTC), 240 h forecast (00 UTC), 360 h
forecast (Saturdays only)
- Operational since Oct. 14 1998
- Global Variational Assimilation System
- Operational since June 18 1997
- Eta-level analysis in June 2000
- TOVS, ACARS/AMDAR ingestion in Sept 2000
- Extended to 4D-Var in March 2005
- Ensemble prediction forecast system (Reference)
- 16 "perturbed" + 1 unperturbed (control) 240-h
forecasts once per day
- 8 perturbed forecasts with the global spectral model
(SEF) - T149L41 (4 forecasts), T149L23 (the other 4
forecasts) - different physics parametrizations
- 8 perturbed forecasts with the GEM model - uniform
configuration, 1.2 degrees horizontal resolution, 28
eta levels; different physics
parametrizations
- Experimental/operational since Jan. 24 1996
- Monthly and seasonal forecasts (Latest
products,
Reference) (PDF Version)
- monthly forecast: temperature anomaly outlooks (under,
over and near the normal) - GEM model (1.875 degrees
horizontal resolution, 50 levels) - issued twice a
month
- three-month seasonal forecasts: 0 lead-time (GEM model and GCM II) produced once a month.
3, 6, and 9-month lead-time (using statistical
methods) produced every three months.
- Atmospheric transport models: the Trajectory model and the
Canadian Emergency Response Model (Reference,
(PDF Version) Environmental
Emergency Response Division)
- used in case of environmental emergencies as diagnostic
tools
DATA ASSIMILATION & INITIALIZATION
- Uninterrupted series of global analyses at main synoptic
hours (00Z, 06Z, 12Z, 18Z)
- Observation misfit obtained by First Guess at Appropriate
Time (FGAT) from full-resolution model integration; The
tangent-linear of the GEM global model and its adjoint, with a
set of simplified physical parametrizations, are used to
propagate the analysis increment and the gradient of the cost
function over the six-hour assimilation window.
- T108 spectral resolution
- 28 eta levels
- Horizontal interpolation of increments on global model's
grid. Analysis levels coincide with model eta levels,
making vertical interpolation unnecessary.
- Model-error statistics derived from ensemble prediction of
short-term lagged forecasts (NCEP 24-48 method)
- Digital filter initialization
GEM MODEL DYNAMICS
- Hydrostatic primitive equations
- Discretisation:
- time -- implicit two time-level semi-Lagrangian scheme;
time step = 2700 sec
- space -- 3D finite elements
- Boundary conditions:
- periodicity in the horizontal
- No motion across eta=0,1 surfaces
- global uniform lat-lon grid with computational poles
rotated with respect to geographic poles.
- 0.9° horizontal resolution
- 401 X 200 grid points in the horizontal
- 28 eta levels, top at 10 hPa
 no horizontal diffusion on prognostic variables,
except in the vicinity of the computational poles.- Stratospheric sponge
-
Reference (PDF)
MODEL PHYSICS
- Solar and infrared radiation interactive with water vapor,
carbon dyoxide, ozone and clouds
- Prediction of surface temperature over land
- Turbulence in the planetary boundary layer through vertical
diffusion, diffusion coefficients based on stability and
kinetic energy
- Surface layer based on Monin-Obukhov similarity theory
- Shallow convection scheme (non precipitating)
- Kuo-type deep convection scheme
- Sundqvist condensation scheme for stratiform
precipitation
- Gravity wave drag
-
Reference (PDF)
FUTURE
- Higher resolution
- Better defined surface fields
- Refined physics
- New data sources
Created :
1998-10-14
Modified :
2002-12-18
Reviewed :
2002-12-18
Url of this page : http://www.msc.ec.gc.ca
/cmc/op_systems/global_forecast_e.html
The Green LaneTM,
Environment Canada's World Wide Web Site.
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