Workpackage Description: WP2
Workpackage mumber: WP2
Start date or starting event: month 0
Lead contractor number: 5
Person Months per Partner: PC2: 6, PC3: 12, PC4: 6, PC5: 36,
                                               PC6: 18, PC8: 6 
Objectives and Input to Work Package
  • To establish the skill with which decadal fluctuations in the Atlantic ocean during the second half of the twentieth century can be simulated in state-of-the-art ocean GCMs forced with observed surface fields.
  • To elucidate the mechanisms responsible for the formation, propagation and decay of dynamic and thermodynamic decadal-timescale anomalies in the Atlantic ocean.
  • To establish how skill varies between different models, and what resolution is required to simulate the observed fluctuations.
Input to WP2: analyses of observed surface fields; results from WP1 describing air-sea flux anomalies associated with SST forced variability.
Description of work
Partners 2, 3, 5 and 8 will perform multidecadal integrations of five different ocean GCMs (see 10.1, Table 2 rows 1-5). The model structure, configuration, grid systems, sea-ice representations, resolution and integration schemes differ, yielding a unique set of complementary rather than duplicate simulations. The models will be forced with 12 hourly NCAR/NCEP atmospheric 10m wind, 2m air temperature, 2m humidity, total cloudiness, precipitation and sea level pressure reanalysis fields for the period 1958-1998. The simulated fields will be compared with the recently compiled Woods Hole `Hydrobase', other available data sets, and results from a data assimilation experiment performed by Partner 6. 

The skill with which the models are able to simulate the major observed dynamic and thermodynamic decadal scale anomalies will be analysed using a common diagnostic framework. The mechanisms responsible for the formation, propagation and decay of these anomalies, including variability in the gyre and thermohaline circulations and in the meridional transport of heat will be investigated. Particular emphasis will be given to the oceanic regions which were found in WP1 to significantly influence the atmosphere. 

Additional, idealised, experiments will be performed to further elucidate mechanisms. Partner 8 will investigate the mechanisms of potential coupled modes by forcing their ocean model with the patterns of atmospheric variability that WP1 suggests arise in response to decadal changes in SST. Partner 4 will use an ocean GCM in an idealised configuration to elucidate how the meridional heat transport by gyre and mean meridional overturning circulations interact and adjust to changes in atmospheric forcing. 
Description of work (continued)
Partner 5 will investigate how model skill varies with model resolution by repeating integrations at three different spatial resolutions (see Table 2), and will assess sensitivity to model formulation by comparing results from the different models. 
Deliverables
     
    D7 Simulation of the variability in the North Atlantic Ocean during 1958-1998 using five different ocean GCMs.
    D8 Assessment of the skill with which observed decadal fluctuations in the Atlantic ocean can be simulated.
    D9 Elucidation of the mechanisms responsible for the formation, propagation and decay of dynamic and thermodynamic decadal-timescale anomalies in the Atlantic ocean.
    D10 Analysis of how and why simulation skill depends on ocean model formulation including model resolution.
Milestones and expected result
Month 18: Multidecadal model integrations complete.
Month 30: Idealised model integrations compete.
Month 34: Analysis of integrations complete.

 

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On 28 Sep 2000, 16:30.