1. Forecast system version

System name: CMCC-SPS4 

First operational forecast run: 1st August, 2025

2. Configuration of the forecast model

Is it a coupled model YES

Coupling frequency: 
Atmosphere-Ocean: 60 minutes (every second full time-step of atmospheric model)

Atmosphere-Land: 30 minutes (also full time-step of atmospheric model)

Atmosphere-Sea Ice: 30 minutes (also full time-step of atmospheric model)

Detailed documentation:

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

2.1 Atmosphere and land surface

Model

CESM2.3 - CAM6 (Atmosphere)

CESM2.3 - CLM 5.1(Land surface)

Horizontal resolution and grid1/2° lat-lon approx
Atmosphere vertical resolution83 levels in the vertical
Top of atmosphere0.01 hPa approx.
Soil levels (layers)

25 
(20 soil layers plus 5 bedrock layers)

Layer 1 (soil): 0-0.020m 

Layer 2 (soil): 0.020-0.060m 

Layer 3 (soil): 0.060-0.0120m

Layer 4 (soil): 0.0120-0.200m

Layer 5 (soil): 0.200-0.320m

Layer 6 (soil): 0.320-0.480m

Layer 7 (soil): 0.480-0.680m

Layer 8 (soil): 0.680-0.920m

Layer 9 (soil): 0.920-1.200m 

Layer 10 (soil): 1.200-1.520m

Layer 11 (soil): 1.520-1.880m

Layer 12 (soil): 1.880-2.280m

Layer 13 (soil): 2.280-2.720m

Layer 14 (soil): 2.720-3.260m

Layer15 (soil): 3.260-3.900m

Layer 16 (soil): 3.900-4.640m

Layer 17 (soil): 4.640-5.480m

Layer 18 (soil): 5.480-6.420m

Layer 19 (soil): 6.420-7.460m 

Layer 20 (soil): 7.460-8.600m

Time step

Main (Physics) Time-step: 30 minutes.

“Tracer” Advection Time step: 20 minutes 
(2/3 of the Physics time step)

Fluid-Dynamics Time step: 10 minutes
(1/3 of the Physics time step).

Detailed documentation:

CAM Model documentation: https://www.cesm.ucar.edu/models/cam 

CLM Model documentation: https://www.cesm.ucar.edu/models/clm 

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

2.2 Ocean and cryosphere

Ocean model

NEMO v4.2

Horizontal resolution1/4°
Vertical resolution75 levels in the vertical
Time step20 minutes
Sea ice modelCICE6
Sea ice model resolution1/4°
Sea ice model levels

8 ice layer + 3 snow layers

(5 ice categories)

Wave modelNO
Wave model resolutionN/A

Detailed documentation:

Nemo Model documentation: https://sites.nemo-ocean.io/user-guide/

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

3. Initialization and initial condition (IC) perturbations

3.1 Atmosphere and land


HindcastForecast
Atmosphere initialization
EDAEDA
Atmosphere IC perturbations1010

Land Initialization

Forced monthly run from three continuous transient simulations started in January 1960, with atmospheric forcings provided by 3 different EDA analyses 

Forced monthly run from three continuous transient simulations started in January 1960, with atmospheric forcings provided by 3 different EDA analyses

Land IC perturbations33
Soil moisture initializationFrom land initializationFrom land initialization
Snow initializationFrom land initializationFrom land initialization
Unperturbed control forecast?NONO
Horizontal resolution of perturbation N/AN/A
Perturbations in +/- pairs NONO
Data assimilation method for control analysis N/AN/A

Detailed documentation:

For more details on ERA5 and EDA: Hersbach et al.  (2020) DOI: https://doi.org/10.1002/qj.3803; Isaksen et al. (2010) DOI: 10.21957/obke4k60

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

3.2 Ocean and cryosphere


HindcastForecast
Ocean initializationC-GLORS
Global Ocean 3D-VAR
C-GLORS
Global Ocean 3D-VAR
Ocean IC perturbations49
Unperturbed control forecast?YESYES

Detailed documentation:

More details on ocean and sea-ice data assimilation:  Storto and Masina (2016) DOI: https://doi.org/10.5194/essd-8-679-2016; Cipollone et al. (2023) DOI: https://doi.org/10.5194/egusphere-2023-254

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

4. Model uncertainties perturbations:

Model dynamics perturbations

NO

Model physics perturbationsYES (Ocean Model only, only during perturbed data assimilation cycles)

If there is a control forecast, is it perturbed?

There is no control forecast

Detailed documentation:

More details on ocean DA perturbations: Storto and Andriopoulos (2021) DOI: https://doi.10.1002/qj.3990

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

5. Forecast system and hindcasts


Forecast frequencyMonthly
Forecast ensemble size50
Hindcast years1993-2022
Hindcast ensemble size30
On-the-fly or static hindcast set?static

6. Other relevant information

The 10 atmospheric perturbed initial conditions, the 3 land perturbed initial conditions and the 9 (4 in hindcast) ocean initial conditions (8/3 perturbed plus the unperturbed in forecast/hindcast mode respectively) are combined to yield 270 (120 in hindcast mode) possible perturbed forecast system initial conditions from which 50 initial conditions uniquely defined (30 in hindcast mode) are randomly chosen, to produce the Forecast Ensemble.

Detailed documentation:

CMCC technical documentation: Sanna et al. (2025) CMCC Technical Note n.301 DOI: https://doi.org/10.25424/cmcc-dkcv-fs25 

7. Where to find more information

Sanna, A., A. Borrelli, P. Athanasiadis, S. Materia, A. Storto, S. Tibaldi, S. Gualdi, 2017: CMCC-SPS3: The CMCC Seasonal Prediction System 3. Centro Euro-Mediterraneo sui Cambiamenti Climatici. CMCC Tech. Note RP0285, 61pp.  https://www.cmcc.it/publications/rp0285-cmcc-sps3-the-cmcc-seasonal-prediction-system-3

Gualdi, S., A. Sanna, A. Borrelli, A. Cantelli, M. del Mar Chaves Montero, S. Tibaldi, 2020: The new CMCC Operational Seasonal Prediction System SPS3.5. Centro Euro-Mediterraneo sui Cambiamenti Climatici. CMCC Tech. Note RP0288, 26pp.  DOI:  https://doi.org/10.25424/CMCC/SPS3.5

Sanna, A., S. Gualdi, M. Benassi, A. Borrelli, D. Peano, M. Hashemi Devin, A. Cipollone and S. Tibaldi, 2025: The new CMCC Seasonal Prediction System SPS4. CMCC Tech. Note n. 301,  31 pp. DOI:   https://doi.org/10.25424/cmcc-dkcv-fs25