1. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 1 Background WGOMD is about to discuss experimental setup to asses ocean model performance in the representation of the inter-annual variability. Possibility of X-Panel interaction and feedback. The GCMS have large errors in the Pacific basin and ENSO, and large uncertainty about the causes. Suggestion: to conduct, in addition to the “MAIN” experiment, a series of sensitivity ocean-only experiment that could give guidance on which elements are key for improvement of the Pacific climate simulations. As additional information:  Seasonal forecasts is an ideal test bed to asses the quality of the GCMS used in future climate projections: oNeed ocean initial conditions to carry out experiments oNot all the groups have ocean data assimilation systems in place. The “MAIN” experiment may be used as initial conditions in coupled model forecasts. => The “MAIN” experiment may be used as initial conditions in coupled model forecasts.

2. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 2 Questions from the Pacific Panel There are known model deficiencies in the representation of the Pacific climate:  Upwelling off the South American Coast (winds, resolution…?)  Cold tongue penetrating too far west (winds? momentum mixing…?)  Too weak/too strong east-west slope of the thermocline  Equatorial heat content (IT/meridional transport, vertical mixing)  … Is it possible to say which are the dominant source of error?  Forcing fields?  Model parameterizations/configuration?  Model resolution?  Parameterization of air-sea interaction?

3. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 3 Suggestion Conduct a long ocean model simulation (20-40 years) with a variety of models, using inter-annually varying atmospheric forcing. This will be the “MAIN” integration, long integration can be used as:  a reference experiment to diagnose and answer some of the above questions (see later)  To provide initial conditions for concerted seasonal forecast experiments.? Conduct additional integrations with each model if possible (no compulsory), to test sensitivities.  Different forcing fields  Different resolution  Different parameterization, bulk formulae, …. It could be good to see these sensitivities from more than one model.

4. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 4 Sensitivities: Compute and Compare Sensitivity to Forcing fluxes: Sensitivity to Resolution: Sensitivity to Model: Sensitivity to Bulk Formula: Sensitivity to P-parameterization:

5. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 5 Example: Diagnosing the sources of uncertainties in the Ocean Analysis intercomparison project organized by GSOP.  Analyses with and without data assimilation  Different analyses use different forcing fields  Different analyses use different models  Models have different resolutions The analyses are clustered according to some criteria, and the standard deviation of the cluster is used as a measure of uncertainty.

6. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 6 Sources of Uncertainty in GSOP ocean analsysis intercomparison All Forcing is ERA40 ERA40-No data assimilation ERA40-With data assimilation

7. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 7 Assimilation and Uncertainty T300 Long period 1956-2005: A large source of uncertainty are the forcing fluxes. 1956-2005 EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL ALL ERA40 as FORCING OCEAN MODEL ASSIMILATION SCHEME FORCING~ ALL – ERA40 Sources of Uncertainty in GSOP ocean analysis intercomparison

8. CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 8 The sensitivity experiments can be done and diagnosed within each group without need of big volumes of “data” transfers. Not all the groups need to carry “all” and the same the sensitivity experiments. It would be interesting to measure the sensitivities both in in the mean state and in the interannual variability. Other basin panels will be interested in the outcome,