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JMA routinely operates Ensemble Prediction Systems (EPSs) to support from medium-range to seasonal prediction. In JMA, the Global Ensemble Prediction System (Global EPS; GEPS) is operated to support for issuing typhoon information as well as one-week, two-week and one-month forecasts, while the Seasonal Ensemble Prediction System (Seasonal EPS) is operated to support issuing three-month and warm/cold season forecasts as well as El Niño monitoring and outlook.
The numerical prediction model used in the Global EPS is an atmospheric general circulation model (AGCM) that is a low-resolution version of the Global Spectral Model (JMA-GSM) used for global deterministic numerical weather prediction. The numerical prediction model used in the Seasonal EPS is a coupled ocean-atmosphere general circulation model (CGCM), which consists of the AGCM (based on a low-resolution version of the GSM) and the ocean general circulation model (OGCM).
The specifications of the Global EPS for one-month prediction and the Seasonal EPS are shown in the following table.
| Global EPS for one-month prediction | Seasonal EPS (JMA/MRI-CPS3) | |
| Last upgrade | March 2023 | February 2022 |
| Model | Atmospheric general circulation model (AGCM) with 2 Tiered SST approach | Coupled ocean-atmosphere general circulation model (JMA/MRI-CGCM3) |
| Atmospheric general circulation model (AGCM) |
JMA-GSM Horizontal resolution: TQ479 (approx. 27 km)(up to 18 days), TQ319 (approx. 40 km)(after 18 days) Vertical levels: 128 levels up to 0.01 hPa |
JMA-GSM with wide-ranging updates for CPS3 Horizontal resolution: TL319 (approx. 55 km) Vertical levels: 100 levels up to 0.01 hPa |
| Oceanic general circulation model (OGCM) |
N/A | MRI.COM Horizontal resolution: 0.25º x 0.25º Vertical levels: 60 levels |
| Integration range | 34 days | up to 7 months |
| Initial conditions | Atmosphere: JMA Global Analysis Ocean: N/A Land: JMA land surface analysis |
Atmosphere: JMA Global Analysis Ocean: MOVE/MRI.COM-G3 (Low-res. 4DVAR + High-res. downscaling) Sea ice: MOVE/MRI.COM-G3 (3DVAR) Land: Offline model runs (forced by JRA-3Q and JMA Global Analysis) |
| Boundary conditions | Sea Surface Temperature (SST): Prescribed SSTs using persisted anomaly with daily climatological SST up to 6-day forecast. After that, SST is relaxed to the ensemble-mean SST operationally predicted by JMA's coupled Seasonal EPS Sea ice: Prescribed sea ice concentration using persisted anomaly with daily climatological sea ice concentration |
SST: One-tier method Sea ice: Interactive sea ice model |
| Ensemble Perturbation method | Combination of Singular vectors (SVs) and Local Ensemble Transform Kalman Filter (LETKF), stochastic physics scheme, SST perturbations and Lagged Average Forecast (LAF) |
Combination of Breeding of Growing Modes (BGM), stochastic physics scheme and Lagged Average Forecast (LAF) |
| Ensemble size | 50 | 51 |
| Freq. of model product creation | Once a week (Model operation) |
Once a month (around 20th of every month) (Model operation) |
| Hindcast period | Jan 1991 - Dec 2020 | Jan 1991 - Dec 2020 |
| Hindcast ensemble size | 13 / initial date Initial dates: 15th and the end of calendar month |
10 / month |