Workpackage Description: WP3
Workpackage mumber: WP3
Start date or starting event: month 0
Lead contractor number: 3
Person Months per Partner: PC1: 24, PC2: 24, PC3: 18, PC4: 18,
                                               PC6: 18, PC8: 18 
Objectives and Input to Work Package
  • To elucidate the mechanisms responsible for decadal fluctuations in the climate of state of the art coupled models, and to assess by detailed comparison with the latest observational datasets the extent to which these mechanisms are realistic.
  • To improve the European capability for forecasting decadal fluctuations in Atlantic-European climate by developing forecasting systems based on coupled ocean-atmosphere models, and by investigating techniques for initialising decadal forecasts.
  • To provide a quantitative assessment of the predictability of decadal fluctuations in Atlantic-European climate.
Input from WP1: regional and seasonal sensitivity of the atmosphere to SST anomalies; feedback of atmospheric response onto the ocean. 

Input from WP2: dynamics of low frequency SST variability in sensitive regions. 
Description of work
Four partners will perform (3 and 8) or provide (2 and 6) multi-century control simulations with four different coupled models (see Table 3). Partner 2 will coordinate the analysis of these control simulations by partners 1, 2, 3, 4, 6 and 8. The results will be compared with observational data sets to elucidate the mechanisms responsible for decadal fluctuations in climate. Results from WP1 and WP2 will guide this analysis. A common framework of diagnostic/statistical analysis will be developed and applied to both the model results and the observations. Particular emphasis will be given to the role of tropical/extra-tropical interactions in the atmosphere and ocean, the role of Gulf Stream variability and the role of air-sea fluxes in the amplification and damping of sea surface temperature anomalies. Partner 4 will perform a lagged SVD (Singular Value Decomposition) analysis to all the simulations to elucidate the nature of causal relationships between the ocean-atmosphere, and will compare the model simulations with 100-year time series of observations 
To identify and understand the mechanisms of decadal variability in the different coupled models it is anticipated that a number of idealised sensitivity studies will also be needed. A facility for restricting active ocean-atmosphere coupling to limited regions of the ocean (Partner 1, see 10.1, Table 2) will assist especially this identification.
Description of work (continued)
The second part of this work package addresses directly decadal predictability and prediction. Partners 1, 2, 3, 6 and 8 will perform prediction experiments with all the coupled models listed in Table 3. Experimental predictions will be made from initial conditions selected from the control integrations following the methodology of Griffies and Bryan (1997). These initial conditions will then be perturbed either in the atmosphere or the ocean or in both components. The divergence of the trajectories from the perturbed initial sates provides a measure of the predictability of the coupled system. Typical ensemble sizes will include 10 members for each set of initial conditions, and each member will be integrated for at least 10 years. 

A common diagnostic framework will be used to quantitatively assess the decadal predictability in each model, and to compare the models. The predictability of different components of the coupled system: the atmosphere, the upper ocean, and the deep ocean, will be explored. 

Partners 2 and 6 will investigate how oceanic data assimilation can improve decadal forecasts. Partners 2, 3 and 6 will investigate techniques (e.g. `breeding') to generate initial perturbations for decadal forecasts.
Deliverables
     
    D11 Simulations of decadal variability in four coupled GCMs.
    D12 A common set of diagnostic/statistical tools for use in the analysis of the coupled model output and observational data.
    D13 Documentation of the characteristics of decadal variability, and elucidation of the mechanisms responsible, in each of the coupled model simulations, and a comparison with observations from the historical record.
    D14 A quantitative assessment of the decadal predictability of decadal fluctuations in Atlantic-European Climate.
    D15 Comparison of the potential predictive skill in the Atlantic-European sector of each of the four coupled GCMs.
    D16 Recommendations for future priorities in the development of systems for decadal climate prediction.
Milestones and expected result
Month 18: Control simulations complete 
Month 30: Analysis of control simulations complete 
Month 30: Predictability experiments complete 
Month 34: Analysis of predictability experiments complete 

 

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On 28 Sep 2000, 16:30.