Tropical Coupled Feedbacks and Climate Variability

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Tropical Coupled Feedbacks and Climate Variability
Ben Kirtman1,2 and Randy Wu2 1George Mason
University and 2Center for Ocean-Land-Atmosphere
Studies
Acknowledgement Emilia Jin (GMU)
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Indian Monsoon Global Ocean Teleconnections
Why do the (uncoupled) AGCMs Fail? Hypothesis
Coupled Air-Sea Interactions?
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Start with Coupled Model that Reproduces Observed
Relationship
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Monsoon
Remote Teleconnections
Remote Teleconnections
ENSO

• ENSO Impacts Monsoon Tropical Wide Shifts in
  Circulation (Importance of Indian Ocean)
• Monsoon Impacts ENSO Large Scale Heating Anomaly
  Impacts
• Pacific Winds, Which Impacts Subsequent Evolution
  of
• ENSO (Lag-Lead Correlation)

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Monsoon
Remote Teleconnections
Remote Teleconnections
ENSO

• ENSO Impacts Monsoon Tropical Wide Shifts in
  Circulation (Importance of Indian Ocean)
• Monsoon Impacts ENSO Large Scale Heating Anomaly
  Impacts
• Pacific Winds, Which Impacts Subsequent Evolution
  of
• ENSO (Lag-Lead Correlation)

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Monsoon Forced Circulation Anomalies
Zonal Wind
Climotological Sea Surface Temperatures
Zonal Wind Stress
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Observations
Weak Monsoon Enhances Warming in Pacific
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Model
Weak Monsoon Enhances Warming in Pacific
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Observations
How a Variable Monsoon Impacts an Ongoing Cold
Event
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Model
How a Variable Monsoon Impacts an Ongoing Cold
Event
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Observations
Normal SST Wet Monsoon
Normal SST Dry Monsoon
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Model
Normal SST Wet Monsoon
Normal SST Dry Monsoon
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Monsoon
Remote Teleconnections
Remote Teleconnections
ENSO

• ENSO Impacts Monsoon Tropical Wide Shifts in
  Circulation (Importance of Indian Ocean)
• Monsoon Impacts ENSO Large Scale Heating Anomaly
  Impacts
• Pacific Winds, Which Impacts Subsequent Evolution
  of
• ENSO (Lag-Lead Correlation)

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Indian Ocean Forcing Dominates the Monsoon
Response
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Is This Enough?

• JJAS ENSO Impacts Monsoon (Indian Ocean)
• Subsequent Seasons Monsoon Impacts ENSO (Tropical
  Pacific Circulation)
• ? Uncoupled AGCM Should, at Least, Recover
  Contemporaneous Correlation
• But, It Doesnt

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Hypothesis

• Coupled Air-Sea Interaction Essential for
  Capturing Monsoon-Global SST Teleconnections
• Latent Heat Flux SST Feedbacks
• Modifies Competition Between Local vs. Remote
  Influences (Indian Ocean)
• Test Perfect AMIP
• Prescribe Exactly Coupled Model SST
• But with Perturbed Atmospheric Initial State
• With Identical Atmospheric Initial Conditions the
  Coupled Model Solution is Recovered Exactly
• 50 Year Simulation

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Global SST-Monsoon Correlation Perfect AMIP
Overlapping 50-Year Period
Global SST-Monsoon Correlation Coupled Simulation
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Regional Coupling Experiments

• Specify Indian Ocean Coupled Model Climatology
  Decoupled Indian Ocean
• Specify Indian Ocean Coupled Model Anomalies
  Forced Indian Ocean
• Specify Pacific Ocean Coupled Model Climatology
  Decoupled Pacific Ocean
• Specify Pacific Ocean Coupled Model Anomalies
  Forced Pacific Ocean

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De-Coupled Indian
Forced Indian Ocean
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Prescribed SSTs in Pacific is OK, but Coupled
Interactions in Indian Ocean Required
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North IO
West North Pac
Local Lag-Lead Regression Between SST
and Precipitation Latent Heat Flux SST
Coupled Model
Regionally Prescribed SST
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Local Internal Dynamics Interfering With Remote
Teleconnections
Monsoon
Remote Teleconnections
Remote Teleconnections
ENSO

• ENSO Impacts Monsoon Tropical Wide Shifts in
  Circulation
• Monsoon Impacts ENSO Large Scale Heating Anomaly
  Impacts
• Pacific Winds, Which Impacts Subsequent Evolution
  of
• ENSO (Lag-Lead Correlation)

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Ratio of Precipitation Standard Deviation (JJAS)
sPrescribed Indian/sControl
Precipitation Variance Increases With
Prescribed SST
sPrescribed Pacific/sControl
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JJAS Precipitation EOF1 1950-2002
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• Prescribing Global SSTs (even from the CGCM)
  Fails to Capture Monsoon-Global SSTA
  Teleconnection
• Regional Coupling Experiments
• Prescribed Pacific and Coupled Indian Ocean
  Re-Captures the Monsoon-SST Co-Variability
• How Do the Coupled Feedbacks Impact the
  Variability?
• Changes in Variability over Warm Oceans
• Ocean Forcing Atmosphere vs. Atmosphere Forcing
  Ocean
• Relationship Between Local SST, SST Tendency,
  Latent Heat Flux and Rainfall

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Conceptual Model
Atmos ? Ocean
ltHF,(dSST)/dtgt
ltHF,SSTgt
Ocean ? Atmos
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Conceptual Model
Atmos ? Ocean

• Atmosphere Forcing Ocean
• ltHF(t), SST(t) gt lt 0
• ltHF(t), d(SST(t))/dtgt lt0

ltHF,(dSST)/dtgt
ltHF,SSTgt
Ocean ? Atmos

• Ocean Forcing Atmospere
• ltHF(t), SST(t) gt gt 0
• ltHF(t), d(SST(t))/dtgt gt 0

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GFSST2 Latent Heat Flux SST (Tendency) Point
Correlation
LHF-SST
Obs SST
OBS
AGCM
LHF-SST Tendency
Obs SST
OBS
AGCM
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Latent Heat Flux SST (Tendency) Point
Correlation
LHF-SST
CGCM SST
CGCM
AGCM
LHF-SST Tendency
CGCM SST
CGCM
AGCM
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ltHF,SSTgt
Conceptual Model Ocean ?Atmos
ltHF,dSSTgt
GSSTF2 Observational Estimates
Area Averaged Fields Eastern Equatorial Pacific
from GCMs
Prescribed SST is Reasonable In Eastern
Equatorial Pacific
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Conceptual Model Atmos ?Ocean
ltHF,dSSTgt
ltHF,SSTgt
GSSTF2 Observational Estimates
Area Averaged Fields Central Equatorial Pacific
CGCM Variability is too Strongly SST Forced
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Conceptual Model
ltHF,dSSTgt
ltHF,SSTgt
GSSTF2 Observational Estimates
Area Averaged Fields North Indian Ocean
CGCM is Over Emphasizing Atmosphere Forcing Ocean
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What About CFS?
CFS
CMAP
Station Data
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Conclusions

• JJAS ENSO Impacts Monsoon (Indian Ocean SSTA
  Required)
• Subsequent Seasons Monsoon Impacts ENSO (Tropical
  Pacific Circulation)
• Teleconnections Sensitive to Strength of Local
  Internal Dynamics
• Latent Heat Flux SST Feedbacks has an Atmospheric
  Damping Effect in Warm Tropical Oceans
• Importance of Coupled Feedbacks for
  Ocean-Atmosphere Co-Variability
• Western Pacific Too Strong Ocean Forcing
  Atmosphere

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Stochastic (in space and time) Heat Flux Forcing
in the Western Tropical Pacific
Heat Flux SST Correlation