IndoPacific Oceanic Teleconnections

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Indo-Pacific Oceanic Teleconnections

• Wenju Cai
• 26th Nov. 2007

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A schematic of the Indo-Pacific mean circulation
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Why study the Indo-Pacific oceanic teleconnection?

• Indo-Pacific variability influences rainfall
  variations, rainfall prediction and future
  rainfall projections.
• Multi-decadal Pacific variability could
  pre-condition the IO thermocline, whereby
  influencing the frequency and amplitude of IODs.
• Unless interannual Indo-Pacific teleconnection is
  well simulated, model IODs and their influence on
  rainfall tend to be unrealistic.
• Attribution of climate change requires a
  quantification of the importance of the
  inter-basin exchanges.

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Outlines

• How ENSO discharge recharge signals transmit to
  the Indian Ocean? What are pathways
• Observed multidecadal variability of the
  transmission
• What controls the transmission properties using
  IPCC AR4 models
• Conclusions

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Transmission through the Equatorial Pacific (EP)
pathway
WA
Clark, JGR, 1991 Potemra et al., JPO, 2002
Wifffels and Meyers, JPO, 2004
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Transmission through the off-equatorial North
Pacific (NP) pathway
Munk-Kelvin Waves
larger f, small velocity
Div.
Conv.
L
Deepened
Shallow
Equator
Godfrey, JPO, 1975 McCreary, Mon. Wea. Rev.
1983 Cai et al. 2005
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The transmission to WA involves both pathways
and is strong since 1980
Post-1980
Pre-1980
Before 1980, little is transmitted
Before 1980, ENSOs are week and more
equatorially confined
Jin 1997 Meinen McPhaden 2000
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Two controlling factors

• Meridional extent of ENSO
• Amplitude of ENSO

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post-1980 wide meridional extent of ENSO
anomalies ? NP Rossby waves are involved.
Pre-1980
Post-1980
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The strong ENSO discharge to the Indian Ocean
temperature change
Shi, Ribbe, Cai, and Cowan, GRL, 2007
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Weak ENSO ? Low ENSO Signal/Noise Ratio D20
Signal One standard deviation associated with
Nino3.4
Noise One stand deviation after removing ENSO
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CSIRO Mk3.5 multi-century control Exp. outputs
Fluctuation in the ENSO amplitude 30-year window
Fluctuation in the transmission of ENSO signals
to WA 30-year window
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IPCC AR4 22 models. 4 failed 1 to WA Sumatra
1 to Sumatra
Cor Thermocline Nino3.4 Lag. 3
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IPCC 22 AR4 models 8 simulate transmission via
EP NP pathway 8 simulate transmission via EP
only
EP only
NPEP
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Dependence on the strength of ENSO signal
Lag 3 Nino3.4 and WA heat content
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Dependence on signal to noise ratio
Lag 3 Nino3.4 and WA heat content
Heat content signal/noise ratio at WA
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Dependence on the meridional extent of ENSO
anomaly
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Conclusions

• Transmission of ENSO signals involves two
  pathways EP and NP.
• Broader, stronger ENSOs tend to involve NP Rossby
  waves, hence signals are transmitted via NP
  pathway.
• Stronger ENSOs have a greater signal to noise
  ratio, more detectable.
• These properties are reflected in the inter-model
  variations of the IPCC AR4.
• AR4 models simulate a cold tongue that is too
  narrow, underestimating the importance of the NP
  pathway.

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Thank You