ENSO Prediction and Predictability

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C. Stan, D. Min, K. Pegion
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ENSO Prediction and Predictability

• Two Views of ENSO Predictability
• Linear Damped Stochastically Forced
• Non-Linear Chaotic System
• Practical Predictability
• CGCM Estimates of Prediction Skill
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• CGCM Forecast Predictability
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• Multi-Model Approach
• Testing IPCC Models
• Model Errors

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Understanding Forecast Skill

• What is the Overall Limit of Predictability?
• What Limits Predictability?
• Uncertainty in Initial Conditions Chaos within
  Non-Linear Dynamics of the Coupled System
• Uncertainty as the System Evolves External
  Stochastic Effects
• Model Dependence?
• Model Error

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ENSO Damped or Unstable?

• Damped
• Linear Dynamics
• Non-Linearity ? Noise
• Noise Amplitude Unrelated to Signal
• Non-Normality and Spatial Structure of Noise
• Limit of Predictability (12 Months)
• Variations in Predictability and ENSO Amplitude
  Modulation Random

• Unstable
• Fundamental Non-Linearity
• Non-Linear Control of Growth
• Details of Noise Relatively Unimportant
• Signal and Noise Amplitude Dependence
• Limit of Predictability (18 Months)
• Variations in Predictability and ENSO Amplitude
  Modulation Fundamental

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ENSO Prediction and Predictability

• Two Views of ENSO Predictability
• Linear Damped Stochastically Forced
• Non-Linear Chaotic System
• Practical Predictability
• CGCM Estimates of Prediction Skill
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• CGCM Forecast Predictability
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• Multi-Model Approach
• Testing IPCC Models
• Model Errors

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15-member CFS reforecasts
15-member CFS reforecasts
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Are We Fooling Ourselves?

• Empirical Prediction
• Rigorous Cross Validation (Exposed Artificial
  Skill)
• Yet, in Real Prediction Skill Much Lower
• Dynamic Prediction
• Hidden Artificial Skill
• Model Tuning
• No Substitute for Real Prediction

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Understanding Forecast Skill

• What is the Overall Limit of Predictability?
• What Limits Predictability?
• Uncertainty in Initial Conditions Chaos within
  Non-Linear Dynamics of the Coupled System
• Uncertainty as the System Evolves External
  Stochastic Effects
• Model Dependence?
• Model Error

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ENSO Prediction and Predictability

• Two Views of ENSO Predictability
• Linear Damped Stochastically Forced
• Non-Linear Chaotic System
• Practical Predictability
• CGCM Estimates of Prediction Skill
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• CGCM Forecast Predictability
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• Multi-Model Approach
• Testing IPCC Models
• Model Errors

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Effect of Increasing Ensemble Size
From DEMETER (ECMWF)
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ENSO Prediction and Predictability

• Two Views of ENSO Predictability
• Linear Damped Stochastically Forced
• Non-Linear Chaotic System
• Practical Predictability
• CGCM Estimates of Prediction Skill
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• CGCM Forecast Predictability
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• Multi-Model Approach
• Testing IPCC Models
• Model Errors

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CCSM3.0 Jan 1982 IC
CFS Jan 1982 IC
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CCSM3.0 Jan 1983 IC
CFS Jan 1983 IC
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CCSM3.0 Jan 1986 IC
CFS Jan 1986 IC
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CCSM3.0 Jan 1988 IC
CFS Jan 1988 IC
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CCSM3.0 Jan 1997 IC
CFS Jan 1997 IC
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CCSM3.0 Jan 2006 IC
COLA Jan 2006 IC
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Infamous Double ITCZ Problem
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Importance of Coupled Feedbacks
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ENSO Prediction and Predictability

• Two Views of ENSO Predictability
• Linear Damped Stochastically Forced
• Non-Linear Chaotic System
• Practical Predictability
• CGCM Estimates of Prediction Skill
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• CGCM Forecast Predictability
• Probabilistic vs. Deterministic
• Noise Initial Condition vs. Forecast Evolution
• Multi-Model Approach
• Testing IPCC Models
• Model Errors