Workpackage Description: WP1
Workpackage mumber: WP1
Start date or starting event: month 0
Lead contractor number: 2
Person Months per Partner: PC1: 12, PC2: 18, PC3: 6, PC4: 12,
                                               PC7: 36, PC8: 12 
Objectives and Input to Work Package
  • To assess quantitatively the potential predictability of decadal fluctuations in North Atlantic Oscillation (NAO) and other facets of Atlantic-European climate, especially those of interest to potential users.
  • To elucidate the mechanisms through which fluctuations in SST force fluctuations in the atmosphere of the Atlantic-European region and which aspects of observed sea surface temperature (SST) fluctuations are most important.
  • To investigate how and why the atmospheric response to decadal changes in SST varies with season.
  • To investigate how and why the atmospheric response to decadal changes in SST depends on the mean atmospheric state, and on model formulation.
  • To investigate how the atmospheric response to decadal changes in SST could feed back to force the ocean.
A major input to this workpackage will be output from a series of multi-decadal ensemble integrations of atmosphere models forced with observed twentieth century SST and sea ice extents (SIE). Some of these integrations are already underway; others will be performed in the first phase of PREDICATE. 

SST and SIE fields from coupled model simulations will be provided by WP3. Users will provide guidance (via WP4) to focus the analysis of decadal predictability.
Description of work
Partners 2, 3, 7 and 8 will provide or perform multidecadal ensemble integrations, as described above, using four different atmospheric GCMs (see 10.1, Table 1). The minimum ensemble size is four. 

Partners 2 and 1 will coordinate the analysis of these integrations by partners 1, 2, 3, 4, 7 and 8. The analyses will employ a common set of key diagnostics, including pointwise analysis of potential predictability (e.g. Rowell, 1998) optimal detection of the most predictable components (i.e. space-time patterns), and comparison with reanalysis data sets. 

The diagnostics will be computed for all seasons and potential predictability will be assessed both for standard meteorological variables and for variables of specific interest to users (e.g. the frequency of extreme events). The way in which the atmospheric response feeds back onto the ocean will be diagnosed, and the results will provide input to WP2 and WP3. 
Description of work (continued)
To understand and interpret the results from the multidecadal ensemble integrations partners 1, 2, 3, 7 and 8 will perform additional ensemble experiments with the four atmospheric GCMs. These experiments will be of shorter duration. A basic set of experiments performed with each of the models will be used to study the atmospheric response in each season to the patterns of SST and SIE that analyses of observations, and analyses of the multidecadal experiments, suggest are most important. Further experiments will be done by each partner to assess the relative roles of subtropical and extratropical SST, to assess the nonlinearity of the atmospheric response, and to elucidate the thermodynamic and dynamical mechanisms that are responsible. 

Partner 7 will investigate how the sensitivity of an atmospheric GCM to SST anomalies depends on the mean state of the model. This will be done by comparing the results of identical experiments with different models and by performing additional experiments in which a novel technique is used to reduce the systematic errors in the model mean state. Partner 7 will also use the model simulations to investigate decadal variations in extreme weather events. 

Partners 4 and 7 will investigate the atmospheric response to the decadal fluctuations in SST that arise in the coupled model simulations performed under WP3. 
Deliverables
     
    D1 Quantitative assessment of potential atmospheric decadal predictability in all four seasons.
    D2 Comparison of the potential predictive skill in the each of the four agcms.
    D3 Analysis of how SST-forced decadal fluctuations can feed back to force the ocean.
    D4 Identification of the SST features that have most influence on Atlantic-European Climate.
    D5 Elucidation of the mechanisms via which tropical and higher latitude SST anomalies influence Atlantic-European climate.
    D6 Analysis of how and why the atmospheric response to SST anomalies depends on the atmospheric mean state and on model formulation.
Milestones and expected result
Month 12: Multidecadal ensemble integrations complete.
Month 18: Analysis of multidecadal ensemble integrations complete.
Month 34: Analysis of idealised experiments complete.

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On 28 Sep 2000, 16:29.