1. Forecast system version
System name: GloSea6-GC5.1
First operational forecast run: 3 March 2026
2. Configuration of the forecast model
Is it a coupled model? Yes: Atmosphere, land, ocean and sea-ice.
Coupling frequency: Hourly coupling between atmosphere-land and ocean-sea-ice.
The coupled model Global Coupled 5.1 (GC5.1) is described in Xavier et al., 2023.
2.1 Atmosphere and land surface
| Model | Met Office Unified Model (UM) - Global Atmosphere and Land 9.1 |
|---|---|
| Horizontal resolution and grid | N216: 0.83 degrees x 0.56 degrees (approx 60km in mid-latitudes) |
| Atmosphere vertical resolution | 85 levels |
| Top of atmosphere | 85km |
| Soil levels (layers) | 4 Layer 1 : 0 - 0.1 m |
| Time step | 15 minutes |
Detailed documentation:
2.2 Ocean and cryosphere
| Ocean model | NEMO v4.0.4 - Global Ocean Sea Ice 9.0 |
|---|---|
| Horizontal resolution | ORCA 0.25 |
| Vertical resolution | L75 |
| Time step | 30 minutes |
| Sea ice model | SI3 - Global Ocean Sea Ice 9.0 |
| Sea ice model resolution | ORCA 0.25 |
| Sea ice model levels | 5 categories + open water |
| Wave model | N/A |
| Wave model resolution | N/A |
Detailed documentation: NEMO documentation
GOSI9: Guiavarc'h et al, 2025.
3. Boundary conditions - climate forcings
| Greenhouse gases | CO2, CH4, N2O, CFC12, HCFC134a - SSP2-4.5 |
|---|---|
| Ozone | CMIP6. Zonal mean climatology 1993-2014. |
| Tropospheric aerosols | Derived from climatology of Model with full aerosol scheme |
| Volcanic aerosols | Backgroud aerosol |
| Solar forcing | CMIP6 |
Detailed documentation:
4. Initialization and initial condition (IC) perturbations
4.1 Atmosphere and land
| Hindcast | Forecast | |
|---|---|---|
| Atmosphere initialization | ERA-5 | Met Office Global Hybrid 4D-VAR |
| Atmosphere IC perturbations | None | None |
| Soil moisture & temperature initialization | Met Office JULES-ERA5 analysis | Met Office JULES-ERA5 analysis |
| Snow initialization | Met Office JULES-ERA5 analysis | Met Office JULES-ERA5 analysis |
| Unperturbed control forecast? | No | No |
Detailed documentation:
Met Office Global Hybrid 4D-VAR: Clayton et al, 2013
ERA5: Hersbach et al., 2020
4.2 Ocean and cryosphere
| Hindcast | Forecast | |
|---|---|---|
| Ocean initialization | GloSea Ocean Sea-Ice Analysis (GS-OSIA) | Forecast Ocean Assimilation Model (FOAM) |
| Ocean IC perturbations | No | No |
| Unperturbed control forecast? | No | No |
Detailed documentation:
The GS-OSIA and the FOAM system both use the Nucleus for European Modelling of the Ocean data assimilation system (NEMOVAR). This is a 3d-VAR data assimilation scheme. The GS-OSIA uses different surface forcing (ERA-5) and observation sets as it is a historical analysis. FOAM uses surface forcing from the Met Office Global NWP model and real-time observations.
The common NEMOVAR system is described in Blockley et al, 2014.
5. Model uncertainties perturbations:
| Model dynamics perturbations | None |
|---|---|
| Model physics perturbations | Atmosphere stochastic physics scheme, SKEB2 |
If there is a control forecast, is it perturbed? | No control |
Detailed documentation:
6. Forecast system and hindcasts
| Forecast frequency | daily |
|---|---|
| Forecast ensemble size | 2 per day |
| Hindcast years | 24 (1993-2016) |
| Hindcast ensemble size | 7 per start date |
| Hindcast start dates | 1, 9, 17, 25 of each month |
| On-the-fly or static hindcast set? | on-the-fly |
7. Other relevant information
Interpolation details
Horizontal Interpolation
Atmosphere: area weighted regrid from N216 to 1x1 degree.
Ocean: uses a two-stage regrid.
- Area weighted regrid fom ORCA025 grid to N216 grid (using same weights as used in model coupling)
- Area weighted regrid from N216 to 1x1 degree
Vertical interpolation
Atmosphere: linear interpolation from the model hybrid height grid onto pressure levels.
8. Where to find more information
GloSea system:
Kettleborough, J. A., and Coauthors, 2025: Global Seasonal Forecasting System 6 (GloSea6): A Large Ensemble Seasonal Forecasting System. Monthly Weather Review, 154, 39–57, https://doi.org/10.1175/MWR-D-25-0007.1.
- Seasonal prediction at the Met Office
- Upgrades to the Met Office Seasonal Forecast System
Model description references:
Bowler, N. E., A. Arribas, S. E. Beare, K. R. Mylne, and G. J. Shutts, 2009: The local ETKF and SKEB: Upgrades to the MOGREPS short-range ensemble prediction system. Quarterly Journal of the Royal Meteorological Society, 135, 767–776, https://doi.org/10.1002/qj.394.
Guiavarc’h, C., and Coauthors, 2025: GOSI9: UK Global Ocean and Sea Ice configurations. Geoscientific Model Development, 18, 377–403, https://doi.org/10.5194/gmd-18-377-2025.
- Xavier, P., and Coauthors, 2023: Assessment of the Met Office Global Coupled model version 5 (GC5)configurations. Met Office 41pp., accessed March 5, 2026, https://centaur.reading.ac.uk/112173/.
Initialisation references:
- Clayton, A. M., A. C. Lorenc, and D. M. Barker, 2013: Operational implementation of a hybrid ensemble/4D-Var global data assimilation system at the Met Office. Quarterly Journal of the Royal Meteorological Society, 139, 1445–1461, https://doi.org/10.1002/qj.2054.
- Blockley, E. W., and Coauthors, 2014: Recent development of the Met Office operational ocean forecasting system: An overview and assessment of the new Global FOAM forecasts. Geoscientific Model Development, 7, 2613–2638, https://doi.org/10.5194/gmd-7-2613-2014
- Hersbach, H., and Coauthors, 2020: The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146, 1999–2049, https://doi.org/10.1002/qj.3803.
Forcing references:
