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| Model | Global Atmosphere 6.0 (GA6): The Unified Model version 8.6 (UM; Williams et al. 2015; Walters et al. 2017). Global Land 6.0 (GL6): Joint UK Land Environment Simulator (JULES; Best et al. 2011; Walters et al. 2017) |
|---|---|
| Horizontal resolution and grid | N216 (~60km in the mid-latitudes) |
| Atmosphere vertical resolution | 85 levels |
| Top of atmosphere | 85 km |
| Soil levels | Four soil levels |
| Time step | 15 minutes |
Detailed documentation:
2.2 Ocean and cryosphere
| Ocean model | NEMO v3.4 (Madec et al. 2023; Megann et al. 2014) |
|---|---|
| Horizontal resolution | ORCA 0.25 |
| Vertical resolution | L75. Level thicknesses range from 1 m near the surface to ~200 m near the bottom (6000-m depth) |
| Time step | 22.5 minutes |
| Sea ice model | CICE v3.1 (Hunke and Lipscomb 2010; Rae et al. 2015) |
| Sea ice model resolution | ORCA 0.25 |
| Sea ice model levels | Five categories and open water (Hunke et al 2010; Rae et al 2015) |
| Wave model | N/A |
| Wave model resolution | N/A |
Detailed documentation: NEMO documentation, CICE documentation
3. Boundary conditions - climate forcings
| Greenhouse gases | Set to observed values up to the year 2005 and after this the emissions follow the Intergovernmental Panel on Climate Change (IPCC) RCP4.5 scenario. |
|---|---|
| Ozone | The SPARC (Cionni et al 2011) observational climatology is used for ozone, which includes a seasonal cycle. |
| Tropospheric aerosols | Climatologies with a seasonal variation (MacLachlan et al. 2015) |
| Volcanic aerosols | N/A |
| Solar forcing | Inter-annual variation |
Detailed documentation:
4. Initialization and initial condition (IC) perturbations
4.1 Atmosphere and land
| Hindcast | Forecast | |
|---|---|---|
| Atmosphere initialization | ERA-Interim (Dee et al. 2011) |
| The Bureau’s 4D-Var analysis (Bureau of Meteorology 2019) | ||
| Atmosphere IC perturbations | See Hudson et al 2017 | See Hudson et al 2017 |
|---|---|---|
Land Initialization |
| Land surface (soil moisture and soil temperature) evolves in response to the atmosphere forcing (i.e., indirect initialisation of the land surface through nudging) | Land surface (soil moisture and soil temperature) evolves in response to the atmosphere forcing (i.e., indirect initialisation of the land surface through nudging) | |
| Land IC perturbations | None | None |
|---|---|---|
| Soil moisture initialization |
| Land surface (soil moisture and soil temperature) evolves in response to the atmosphere forcing (i.e., indirect initialisation of the land surface through nudging) | Land surface (soil moisture and soil temperature) evolves in response to the atmosphere forcing (i.e., indirect initialisation of the land surface through nudging) |
| Snow initialization | ||
|---|---|---|
| Unperturbed control forecast? | None | None |
Data assimilation method for control analysis:
...
Detailed documentation:
4.2 Ocean and cryosphere
| Hindcast | Forecast | |
|---|---|---|
| Ocean initialization |
Weakly coupled ensemble optimal interpolation method (Wedd et al 2022), based on the EnKF-C software (Sakov 2014) | Weakly coupled ensemble optimal interpolation method (Wedd et al 2022) |
| , based on the EnKF-C software (Sakov 2014) |
| Ocean IC perturbations |
|---|
| None | None |
| Unperturbed control forecast? |
|---|
| None | None |
Detailed documentation:
Sakov P. (2014) EnKF-C user guide. arXiv: Computer Science 1410.1233, v1. doi:10.48550/arXiv.1410.1233
5. Model Uncertainties perturbations:
| Model dynamics perturbations | None |
|---|---|
| Model physics perturbations | NoneAtmosphere stochastic physics scheme, SKEB2 (Bowler et al 2009) |
If there is a control forecast, is it perturbed? | No control |
Detailed documentation:
6. Forecast system and hindcasts
| Forecast frequency | Daily |
|---|---|
| Forecast ensemble size | 11 per day out to 6 months 22 per day out to 6 weeks |
| Hindcast years |
| 38 (January 1981- December 2018) | |
| Hindcast ensemble size | 27-member time-lagged ensemble: 3 per start date out to 9 months back 9 days, 6 per start date out to 6 weeks back 3 days (Also see next section) |
|---|---|
| On-the-fly or static hindcast set? | Static |
| Calibration (bias correction) period |
| January 1981- December 2018 |
7. Other relevant information
Hindcast configuration employs a time-lagged ensemble approach in which the number of ensemble members is dependent on the start date of the hindcast.
1) Three-member ensembles (out to 279 days) six times per month on the 1st, 6th, 11th, 16th, 21st and 26th to support climatologies and calibration of the real-time system. Real-time forecasts utilise the closest prior climatology date for bias correction or calibration.
2) A 27-member time-lagged ensemble once per month, valid on the 1st of the month, to support calculation of seasonal skill. This comprises three 279-day ensemble members on 9 successive days (the 1st of the month and the 8 prior days of the previous month).
3) A 27-member time-lagged ensemble twice per month, valid on the 1st of the month and the 16th of the month, to support calculation of multi-week skill. This comprises nine 42-day ensemble members from 3 successive days: (1)on the 1st of the month plus the 2 days prior and (2) on the 16th of the month plus the 15th and 14th.
8. Where to find more information
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