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
JMA operates four numerical wave models: the Global Wave Model (GWM), the Coastal Wave Model(CWM), the Wave Ensemble System (WENS), and the Shallow-water Wave Model (SWM). The GWM,
CWM and WENS are based on MRI-III, which was developed at JMA’s Meteorological ResearchInstitute (MRI), and a major update was made to the current version in May 2007. The WENS has
been operational since June 2016. The specifications of the models are given in the Table.
Model name

Global Wave Model
Coastal Wave Model(GWM)(CWM)
Spectral model (third-generation wave model)

Wave Ensemble System(WENS)

Model type
DateofMay 2007
May 2007
March 2020
implementation
Grid form
Equal latitude-longitude grid on spherical coordinates
Grid interval
0.5° × 0.5°
0.05° × 0.05°
0.5° × 0.5°
(55 km)(5 km)(55 km)Calculation area
Global 75°N – 75°S
Coastal Sea of Japan Global 75°N – 75°S
50°N – 20°N, 120°E –150°E
Grids
720 × 301
601 × 601720 × 301
Spectral
900 (25 frequencies and 36 directions)components
Frequency: 0.0375 – 0.3 Hz; logarithmically divided
direction: 10° intervals
Forecast cycle
4 times a day (every 6 hours)
Twice a day (every 12hours)
Forecast length(12 UTC)
264 hours
132 hours
264 hours(00/06/18 UTC)132 hours
132 hours
Forecasttime
Every 3 hours
Every 3 hours
Every 6 hours
interval
Time step
Advection term: 10 Advection term: 1 Advection term: 10minutes
minuteminutes
Sourceterm:
30 Sourceterm:
3 Source
term:
30
minutesminutesminutes
Assimilation
Surface forcingLateral boundary

Shallow-watereffects
Product

Wave height analyzed using the Objective Wave Analysis System
Initial conditions modified using analysis wave height
Global Spectral Model (GSM) (20 km grid)
GlobalEnsemble
Winds inside typhoons modified using ideal Prediction
Systemgradient wind values (– 72 hours)(GEPS)
27 members
Sea ice: analysis area Sea ice: analysis area Sea ice: analysis area
regarded as land
regarded as land
regarded as land
GWM prediction usedfor boundary spectra
Refraction and bottom friction
Significant wave height, wave period and mean wave direction
Wave components (windsea and two swells) also calculated

Comments-1-The wave model was majorly updated in May 2007, and minor update was in July 2008. In major
updates to the Global Wave Model (GWM) and the Coastal Wave Model (CWM), shallow-water effects
and modification of wind input were implemented in May 2017. In major updates to the Wave
Ensemble System (WENS), the grid resolution was enhanced from 1.25° to 0.5° (from 140 to 55 km)
and shallow-water effects were incorporated in March 2020.
An assimilation scheme developed by JMA for wave models was incorporated into the GWM and theCWM in October 2012. The WENS also uses assimilated initial condition.
JMA began calculating wave components (windsea and swell) for the GWM and CWM on July 20
2016.
The forecast time of GWM is currently up to 5.5 days at 00, 06 and 18 UTC initial runs and 11 days
at 12 UTC.
The wave predicted data of GWM is provided via GTS and WIS. The product is 6 hourly up to 3.5
days (00, 06, 12 and 18 UTC) and 12 hourly up to 8 days (12 UTC).
Reference:
Kohno, N., D. Miura, and K. Yoshita, 2012: The Development of JMA Wave Data Assimilation System.
Proceeding of 12th International Workshop on Wave Hindcasting and Forecasting & 3rd Coastal
Hazard Symposium, H2.
(http://www.waveworkshop.org/12thWaves/papers/full_paper_Kohno_et_al.pdf)-2-