Joint Proposal to WGOMD for a community ocean model experiment

Background Seasonal Forecasts is an ideal test bed to asses the quality of the GCMS used in future climate projections: Need ocean initial conditions to carry out experiments Not all the groups have ocean data assimilation systems in place. 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 proposed experiment could answer some outstanding questions about the key elements needed to improve the representation of the Pacific basin and ENSO.

Questions from the Pacific Panel There are known model deficiencies in the representation of the Pacific climate: Upwelling off the South American Coast Cold tongue penetrating too far west 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?

Proposal Conduct a long ocean model simulation (20-40 years) with a variety of models, using inter-annually varying atmospheric reanalysis (ERA40-ENACT, NCEP-CORE, JMR- 25…). This long integration can be used as: a CNTL experiment to answer some of the above questions (see later) To provide initial conditions for concerted seasonal forecast experiments. Conduct additional integrations with each model (optional), to test sensitivities: Different forcing fields Different resolution Different parameterization, bulk formulae, …. Need to agree the specifications for the CNTL integration.

Sensitivities: Compute and Compare Sensitivity to Forcing fluxes: Sensitivity to Resolution: Sensitivity to Model: Sensitivity to Bulk Formula: Sensitivity to P-parameterization:

Sources of Uncertainty All ERA40 ERA40-No data ERA40-Assim

Assimilation and Uncertainty T300 Long period 1956-2005: Large part of uncertainty comes from forcing fluxes 1956-2005 EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL ALL SAME FORCING (ERA40) OCEAN MODEL ASSIMILATION SCHEME

Sensitivities: preliminary results from ENACT/GSOP MEAN STATE: Equatorial Pacific heat content is model dependent Slope of Pacific Eq. thermocline controlled by winds ERA40 produces weak thermocline slope in most models Too diffuse thermocline in Indian Ocean? Analysis minus Observations Western Pacific Equatorial Indian DATA ASSIM NO DATA ASSIM Mean Assimation Temperature Increment

Strawman for the CNTL integration From spin up, launch the integrations, using daily atmospheric forcing fluxes plus some restoring terms: 3D relaxation to climatology of T and S (~10 year time scale) Strong relaxation to time-varying values of SST (~2-3 days t.s) Relaxation to climatological Surface Salinity (1 year t.s) If free surface, volume preserving constrains. The restoring terms are used to diagnose errors. Atmospheric forcing (daily values): Momentum flux: ERA40 0-24 wind stress Heat flux: ERA40 0-24 solar, latent and sensible heat fluxes. PLUS Strong relaxation to daily values of SST (~2 days time scale) (Reynolds from 1982) Fresh Water flux: ERA40 0-24 PME + ENACT correction Weak Relaxation to climatological SSS (~12 month time scale) If free surface, some volume preserving constrains.

CNTL integration at ECWMF Decent Inter-annual ENSO variability Correlation with altimeter data (1993-2003)

CNTL integration at ECWMF Some MOC variability

CNTL integration at ECWMF As initial conditions, decent forecast skill. S3 Nodata S3 Assim