Specifications (as of 31 December 2020) – an excerpt from the Joint WMO Technical Progress
Report on the Global Data Processing and Forecasting System and Numerical Weather Prediction
Research Activities for 2020

Global EPS specifications for the first 11 days of forecasts
1. Ensemble system
Ensemble (version)
Date of implementation
2. EPS configuration
Model (version)

Global EPS (GEPS)
19 January 2017
Global Spectral Model (GSM2003)

Horizontal
resolution/grid spacing
Verticalresolution(model top)
Forecast length (initialtime)Members

Spectral triangular 479 (TL479), reduced Gaussian grid system, roughly
equivalent to 0.375 × 0.375° (40 km) in latitude and longitude
100 stretched sigma pressure hybrid levels (0.01 hPa)

Couplingto
ocean/wave/sea
icemodels
Integration time step
Additional comments
3. Initial conditions andperturbations
Initialperturbation
strategy
Optimization time inforecast for SV

None

Horizontal resolution ofperturbations

Initial perturbation areaData
assimilation
methodforcontrol
analysis
Initial conditions for
perturbed members
Additional comments
4. Model uncertainty
perturbations
Modelphysics
perturbations
Modeldynamics
perturbations
Additional comments
5. Surface boundaryperturbations

11 days (00, 12 UTC)132 hours (06, 18 UTC)
1 unperturbed control forecast and 26 perturbed ensemble members

720 seconds
None

Singular vectors (SVs) and LETKF
Among three targeted SV areas:
48 hours for Northern Hemisphere (30° – 90°N)
24 hours for Tropics (30°S – 30°N)
48 hours for Southern Hemisphere (90° – 30°S)
SVs:
Spectral triangular 63 (TL63), reduced Gaussian grid system, roughly
equivalent to 2.8125 × 2.8125° (270 km) in latitude and longitude
Perturbations from LETKF:
See the specifications of the LETKF in Global Analysis*
GlobalFour-dimensional variational (4D-Var) for Global Analysis (GA) Control
analysis based on interpolation of high-resolution GA (TL959)
Addition of perturbations to control analysis (SV-based components in +/pairs)
LETKF-based perturbations are produced using a total of 26 six-hour
forecasts starting from the previous LETKF cycle.

Stochastic perturbation of physics tendencyNone

Identical model versions for all ensemble members
Above model uncertainty perturbations not applied to control
forecastingSea surface temperature
perturbations

Perturbations representing climatological distribution of analysis andforecast error of prescribed SST sampled from past realizations ofanalysis increment and forecast error of SST in the same season
None

Soilmoisture
perturbations
Surfacewind None
stress/roughness
perturbations
Othersurface None
perturbations
Additional comments
The above surface perturbations are not applied to the control forecast.
6. Other model details
Surface boundary conditions
Treatment of sea surface Climatological sea surface temperature with daily analysis anomaly
Climatological sea ice concentration with daily analysis anomalyLand surface analysis
Snow depth: two-dimensional optimal interpolation scheme
Temperature: first guess
Soil moisture: climatology
Model dynamics and physics
Land surface and soil
Simple Biosphere (SiB) modelRadiation
Two-stream with delta-Eddington approximation for shortwave (hourly)
Two-stream absorption approximation method for longwave (hourly)
Numerical techniques
Spectral (spherical harmonic basis functions) in horizontal, finite
differences in verticalTwo-time-level, semi-Lagrangian, semi-implicit time integration scheme
Hydrostatic approximation
Planetaryboundary Mellor and Yamada level-2 turbulence closure scheme
layer
Similarity theory in bulk formulae for surface layer
Convection
Prognostic Arakawa-Schubert cumulus parameterization
CloudPDF-based cloud parameterization
Subgrid orography
Low-level blocked-flow drag, gravity wave drag and turbulent orographic
form drag schemes
Non-orographic gravity Spectral gravity wave forcing scheme
wave drag7. Products
Method of calculation (if None
not unique)
Other specifications as None
necessary
8. Further information
Operational contact
globalnwp@met.kishou.go.jp
System documentation https://www.jma.go.jp/jma/jma-eng/jma-center/nwp/nwp-top.htm
URL* See Joint WMO Technical Progress Report on the Global Data Processing and Forecasting System andNumerical Weather Prediction Research Activities for 2020.

Global EPS specifications for forecasts longer than 11 days
Atmospheric model
Integration domain
Horizontal resolution

GSM2003
GlobalSpectral triangular 479 (TL479), reduced Gaussian grid system, roughly
equivalent to 0.375 × 0.375° (40 km) in latitude and longitude for forecasts
up to 18 days
Spectral triangular 319 (TL319), reduced Gaussian grid system, roughly
equivalent to 0.5625 × 0.5625° (55 km) in latitude and longitude for forecasts
longer than 18 days
Vertical levels (model 100 stretched sigma pressure hybrid levels (0.01 hPa)
top)
Forecast time
18 days for initial times every day
34 days for initial times on Tuesday and Wednesday
Ensemble size
50 members (13 at 00 and 12 UTC over the previous two days)