effect of tropical biases on enso simulation and prediction ed schneider and ben kirtman george...
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![Page 1: Effect of Tropical Biases on ENSO Simulation and Prediction Ed Schneider and Ben Kirtman George Mason University COLA](https://reader036.vdocuments.mx/reader036/viewer/2022081519/56649eec5503460f94bfe5cf/html5/thumbnails/1.jpg)
Effect of Tropical Biases on ENSO Simulation and
PredictionEd Schneider and Ben Kirtman
George Mason University
COLA
![Page 2: Effect of Tropical Biases on ENSO Simulation and Prediction Ed Schneider and Ben Kirtman George Mason University COLA](https://reader036.vdocuments.mx/reader036/viewer/2022081519/56649eec5503460f94bfe5cf/html5/thumbnails/2.jpg)
Overview of COLA Research Topics Related to Tropical
Biases
• Basic problem: What causes the ITCZ?
• Why do coupled models have different biases?
• What effect do biases have on ENSO prediction?
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What Causes the ITCZ?
• Kirtman and Schneider, 2000, JAS.• Minimal general circulation: RCE (Radiative-
Convective Equilibrium) or something else? Expect something else if the ITCZ has a dynamically preferred position (e.g. due to Ekman dynamics).– Aqua planet AGCM (T30L18)– Uniform SST everywhere– Meridionally uniform incident solar radiation
• Result: something else.
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Globally Uniform Specified SST:Precipitation Response
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Slab Mixed Layer Ocean
SST
Precip
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Interpretation
• The ITCZ has a preferred location, which leads to a self sustaining large scale general circulation in the absence of meridional forcing.
• Necessary ingredients: convective instability (heating from below) + rotation. Eddy momentum fluxes play a role.
• In our model, the preferred location is the equator (3D) or oscillating around the equator (2D).
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Why Do Coupled Models Have Different Tropical Biases?
• Compare COLA and CCM3 coupled to MOM2 (Schneider, 2002, J. Climate).
• Different annual mean, annual cycle, SI variability.
• Eliminate structural and parameterized differences between the models step by step.
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Annual Means
Precipitation
SST
OBS
COLA
CCM3
COLA minus CCM3
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Annual Cycle of SST in the Equatorial Pacific
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SST Anomalies in the Equatorial Pacific
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Annual Mean SST in the Equatorial Pacific from Experiments
A1 A2 A3 A4
A5 A6 A7 A8
A9 B1 B2 B3 CAC Analysis
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Annual Cycle of SST in the Equatorial Pacific (Experiments)
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Standard Deviation of SST Anomalies in the Equatorial Pacific
(Experiments)
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Effect of Systematic Biases on ENSO Forecasts
• Schneider, DeWitt, Rosati, Kirtman, Ji, and Tribbia, 2003, Mon. Wea. Rev. (submitted).
• Biases in mean translate in forecasts to systematic drift of SST from initial state (obs.) to model climate + initial shock.
• Biases in variability lead to systematic drift in variability away from obs. and towards model climate with a time scale of several months.
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Experiments
• A single 12 month forecast for each Jan. 1 and July 1 observed (ocean) initial state, 1980-1999 (40 cases) for each of 5 coupled model configurations.
• AGCM: COLA V2, ECHAM4.5, CCM3 at T42, 18/19 levels.
• OGCM: MOM3, “IRI” physics, 1x1 L40 or 1.5x1.5 L25, 65S-60N domain.
• GFDL ODA for ocean initial state.
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NINO3 SSTA Correlations
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Systematic Bias E. Pacific SST
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Standard Deviation Simulations in the Equatorial Pacific
COLA med
ECHAM med
CCM med
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Systematic Bias Equatorial Pacific SST Anomalies
Analysis
Consensus
COLA high
COLA med
ECHAM high
ECHAM med
CCM med
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Systematic Bias Equatorial Pacific Heat Content (VAT) Anomalies
Analysis
Consensus
COLA high
COLA med
ECHAM high
ECHAM med
CCM med