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:o Need ocean initial conditions to carry out experimentso Not all the groups have ocean data assimilation systems in place.

=> The “MAIN” experiment may be used as initial conditions in coupled The “MAIN” experiment may be used as initial conditions in coupled model forecasts.model forecasts.

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?

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.

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:

CteBPMRFXF

,,,

CteBPMFRXR

,,,

CteBPRFMXM

,,,

CteRPMFBXB

,,,

CteBRMFPXP

,,,

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.

CLIVAR WORKSHOP. Barcelona 4-6 June 2007: Joint Proposal to WGOMD 6

Sources of Uncertainty in GSOP ocean analsysis intercomparison

EQPAC

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EQATL

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EQIND

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NINO3

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DTRATL

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INDPL

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All

Forcing is ERA40

ERA40-No data assimilation

ERA40-With data assimilation

12m-rm seasonal anom: EQPAC Averaged temperature over the top 300m

1950 1960 1970 1980 1990 2000Time

-1.0

-0.5

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1.0

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allsdv_ensm= 0.269spread= 0.239s/n_ensm = 1.127

era40sdv_ensm= 0.278spread= 0.145s/n_ensm = 1.912

era40-ctrlsdv_ensm= 0.338spread= 0.117s/n_ensm = 2.887

era40-assmsdv_ensm= 0.332spread= 0.085s/n_ensm = 3.910

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

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TRPAC

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TRATL

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NPAC

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NATL

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GLOBAL

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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

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,