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Coupled Initialization Experiments in the COLA Anomaly Coupled Model

Coupled Initialization Experiments in the COLA Anomaly Coupled Model. Ben Kirtman George Mason University and Center for Ocean-Land-Atmosphere Studies. Why Do Coupled Assimilation?. Better State Estimation (Air-Sea Fluxes For Example) Assessing Observing Systems Improve Coupled Model

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Coupled Initialization Experiments in the COLA Anomaly Coupled Model

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  1. Coupled Initialization Experiments in the COLA Anomaly Coupled Model Ben Kirtman George Mason University and Center for Ocean-Land-Atmosphere Studies

  2. Why Do Coupled Assimilation? • Better State Estimation (Air-Sea Fluxes For Example) • Assessing Observing Systems • Improve Coupled Model • Improve Coupled Predictions (Coupled Assimilation != Coupled Initialization)

  3. COLA Perspective • Emphasis Needs to be on Prediction • The Forecast Initialization Procedure Should Account for Two Problems: • Coupled Model Climate Does Not Agree with Observed Climate • Coupled Modes of the Coupled Model are Significantly Different From the Coupled Modes of Nature Approaches: (i) Anomaly Initialization (ii)AnomalyCoupling (iii)Assimilate “Coupled Modes”

  4. Outline • Motivation: • Experimental Prediction: Where do we Stand? • Results From ARCS Project • Results From COLA Anomaly Coupled Model • Initialization Shock and Aliasing Coupled Modes • Identifying Coupled Modes • Mapping Observed Modes onto Model Modes • Coupled Initialization (Nudging) Model Coupled Modes

  5. Is the Best Fit Best For Forecasting? Give More Weight to the Model? Ji et al. (1998) NCEP

  6. Atmos Initialization No Atmos Initialization Persistence Coupled forecast results suggest that some equilibrium between atmosphere and SST required. Schneider et al., 1998; COLA Coupled Model Lead Time (months)

  7. ODA SST Winds and SST Rosati et al., 1997; GFDL

  8. Standard Zebiak-Cane Ocean: FSU Forcing Wind Nudging within the Coupled System Chen et al., 1995, 1997; LDEO

  9. COLA-IRI-GFDL-NCAR Collaboration on Global Coupled Prediction • OGCM: MOM3 with Agreed Upon Physics, High Res. 1.0x1.0x40 ÿ 1/3x1.0x40 Medium Res. 1.5x1.5x25 ÿ 1/2x1.5x25 • AGCM: T42L18: ECHAM4.5 (IRI), COLA, CCM3 • ICs: Ocean: GFDL ODA, 40 Cases: Jan. and Jul. 1980-1999; Atmosphere: Open but taken from long simulation with observed SST. • Coupling: No Flux Corrections or Anomaly Coupling

  10. Problem: Coupled Model Climate Does Not Agree with Observed (ODA) Climate Initialization Shock May Degrade Forecast Skill

  11. Analysis 80-99 Consensus COLA (High) COLA (Med) ECHAM (high) ECHAM (Med) CCM (Med)

  12. Analysis 80-99 Consensus COLA (High) COLA (Med) ECHAM (High) ECHAM (Med) CCM (Med)

  13. COLA ECHAM CCM

  14. Initialization Shock Problem: Coupled Model Climate Does Not Agree with ODA Climate • Fix the Coupled Model • Anomaly Initialization • Empirical Corrections (Anomaly Coupling)

  15. +2 Atmos Initialization No Atmos Initialization Persistence -9 Lead Time (months)

  16. COLA Anomaly Coupled Model • OGCM GFDL MOM3 • 1.5x1.5x25 0.5x1.5x25 • AGCM COLA T42L18 • ICs: • Ocean: GFDL ODA Interpolated to Above Resolution. 80 Cases: Jan, Apr, Jul, Oct. 1980-1999 • Atmosphere: Generated by Running with Observed SSTs. Six Atmospheric Perturbations Generated by Resetting the Calendar and Running for One Week ÿ 6 x 80 Cases = 480 Hindcasts

  17. Problem: Coupled Modes of the Coupled Model are Significantly Different From the Coupled Modes of Nature Even With Anomaly Coupling the Forecast Do Not Have the Right Variability

  18. Initializing the Model Coupled Modes • Identify Model Coupled Modes • Mapping Between Model Modes and Observed Modes • Inserting Mapped Modes into Coupled Model (Coupled Nudging) • Experimental Forecasts

  19. Sub-Surface Temperature Nudging Procedure Where time scale of the damping (a) is 10 days-1 at the surface and 50 days-1 at 250 meters. Linearly decreasing from the surface to 250 meters and constant below 250 meters. Does Nudging Work? - Compare Different Data Assimilation Systems.

  20. Initializing the Model Coupled Modes • Identify Model Coupled Modes • Mapping Between Model Modes and Observed Modes • Inserting Mapped Modes into Coupled Model (Coupled Nudging) • Experimental Forecasts

  21. Identifying Coupled Modes • Analogue Approach • Heat Content Analogues Don’t Work Coupled Modes of Coupled Model are Not the Same as the Observations • Use Long Simulation to Identify “Best Fit” SST Evolution (12 Months) Relate Analogue “Initial State” to Observed Initial State

  22. GFDL ODA Anomaly Coupled Simulation RMSE Best Fit Simulated Heat Content Does Not Match Observations Well

  23. And Then Leads to a Relatively Poor Forecast Forecast Initialized with GFDL ODA Jan1982

  24. Best Fit Initial Heat Content Does Not Make A Good Analogue. Model Modes are Different From Obs What Do The Modes That Fit The Forecast Look Like? Fit SST Evolution to Observations What is Initial Heat Content?

  25. GFDL ODA Anomaly Coupled Simulation RMSE Best Fit Simulated Heat Content Does Not Match Observations Well

  26. Initializing the Model Coupled Modes • Identify Model Coupled Modes • Mapping Between Model Modes and Observed Modes • Inserting Mapped Modes into Coupled Model (Coupled Nudging) • Experimental Forecasts

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