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IndoPacific Oceanic Teleconnections

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post-1980 wide meridional extent of ENSO anomalies NP Rossby waves are ... These properties are reflected in the inter-model variations of the IPCC AR4. ... – PowerPoint PPT presentation

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Title: IndoPacific Oceanic Teleconnections


1
Indo-Pacific Oceanic Teleconnections
  • Wenju Cai
  • 26th Nov. 2007

2
A schematic of the Indo-Pacific mean circulation
3
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.

4
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

5
Transmission through the Equatorial Pacific (EP)
pathway
WA
Clark, JGR, 1991 Potemra et al., JPO, 2002
Wifffels and Meyers, JPO, 2004
6
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
7
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
8
Two controlling factors
  • Meridional extent of ENSO
  • Amplitude of ENSO

9
post-1980 wide meridional extent of ENSO
anomalies ? NP Rossby waves are involved.
Pre-1980
Post-1980
10
The strong ENSO discharge to the Indian Ocean
temperature change
Shi, Ribbe, Cai, and Cowan, GRL, 2007
11
Weak ENSO ? Low ENSO Signal/Noise Ratio D20
Signal One standard deviation associated with
Nino3.4
Noise One stand deviation after removing ENSO
12
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
13
IPCC AR4 22 models. 4 failed 1 to WA Sumatra
1 to Sumatra
Cor Thermocline Nino3.4 Lag. 3
14
IPCC 22 AR4 models 8 simulate transmission via
EP NP pathway 8 simulate transmission via EP
only
EP only
NPEP
15
Dependence on the strength of ENSO signal
Lag 3 Nino3.4 and WA heat content
16
Dependence on signal to noise ratio
Lag 3 Nino3.4 and WA heat content
Heat content signal/noise ratio at WA
17
Dependence on the meridional extent of ENSO
anomaly
18
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.

19
Thank You
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