H. H. H. Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration Masamichi Ohba (Central Research Institute of Electric Power Industry, Abiko, Japan)
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Role of the Indo-Pacific Interbasin Coupling
in Predicting Asymmetric ENSO Transition and Duration
Masamichi Ohba(Central Research Institute of Electric Power Industry, Abiko, Japan)
Masahiro Watanabe(Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan)
J. Climate in press.
Circles: observed strong event
3. Asymmetric impact of IO on ENSO transition
a. Perfect model experiment
Prediction skill of El Nino and La Nina for growth and decay (dash) phase of ENSO
Relationship of forecast skills between the TPO and IO
Coupled-IO simulation from Oct0 to Aug1 :each ensemble
El Nino-Southern Oscillation (ENSO)
Evolution of the Nino 3.4 index
El Nino phase: the IO prediction skill is relatively
collaborated with the following TPO predictability
La Nina phase: the Indo-Pacific interbasin coupling is much weaker than El Nino
Spread of individual
forecast for NIO
ACC of Nino3
The decline of the ACCs swerves to the left
Both the ACCs drop along the one-to-one line
Jin and Kinter (2009,JC)
The La Nina events endure in both simulation& the spread is much small
The difference begins to spread after the spring
Similar asymmetry of the IO-ENSO relationship is found in the 450-yr coupled-IO ctrl run
Coupled-IO hasting the El Niño transitionconsistent with the previous studies.
(e.g., Kug et al. 2006; Ohba and Ueda 2007)
b. Long-term IO-decoupled simulation
Easterly wind anom. in both phase
after their mature phase
From Ohba and Ueda 2009
One-sided lag regression (cont) and correlation (shd) of equatorial SST onto the positive and negative DJF Nino-3.4 index
EPAC only vs IO+PAC
The other half is likely due to direct nonlinear atmospheric response to local CEP forcing
(e.g. Hoerling et al. 2001; Ohba and Ueda 2009)
About half of the ENSO asymmetry
arise from the asymmetry of IO feedback
Surface wind response to SST anom.
AGCM: DJF SST anom.
El Niño：increase the duration period
La Niña：relatively small difference
Anomaly correlation for ensemble mean SST over the tropical Pacific Ocean (TPO)
Reduced WP easterly with
ENSO-related symmetric SST forcing
Asymmetry of WP zonal wind
is significantly reduced !!
TPO: 120°E-90°W, 15°S-15°N
Solid: Ctrl vs coupled-IO
Dash: Ctrl vs decouple-IO
4. Summary and discussion
Skewness of simulated SST and
Tropospheric temp (850-250 hPa)
Coupled-IO extends skillful
prediction about 1.5 year
Nonlinear atmospheric response to SST around the boreal winter-spring is responsible for the ENSO asym.
(Ohba and Ueda 2009)
(Okumura et al. 2011)
Purpose of this study is to evaluate the extent to which the interactive IO
is responsible for the ENSO asymmetry in duration
Decoupled-IO: about 8mon
The skill drops rapidlyas seen in the “spring prediction barrier”
2. Coupled GCM: MIROC5(T42 ver.)
Shade: SST , contour: Toropos. temp
The difference between the CIO vs NIO is very minorin La Niña
The amplitude of the Indian Ocean SST warming is much stronger than that of the cooling.
Asymmetry of ENSO in CMIP3 & 5
Cor. DJF Nino34 vs DJF(+1yr) nino34
How the El Nino transition is accelerated?
When El Nino-direct heating exists in the WP, the IO feedback(easterly anom.) is significantly interfered.
→ The zonal distance is important factor for the ENSO asymmetry
Most remarkable case:
El Nino oct0037 simulation
Remarkable cooling with the anomalous easterlies
Red: El Niño
Blue: La Niña
Effect of the IO feedback is different between El Nino and La Nina
About half of ENSO asymmetry arises from asymmetry of the Indo-Pacific interbasin coupling (the other half is possibly due to nonlinear atmospheric response to local SST in the Pacific as Ohba and Ueda 2009)
Interactive Air-Sea Coupled-IO(CIO) V.S. Decoupled-IO(NIO) by prescribing the clim. SST
a. Idealized twin forecast experiment & b. Long-term NIO experiment (100-yr)
The LBM responses to the heating located on various longitudes well capture the observed relationship.
Enhanced generationof Kelvin wave-like
-> Acceleration of the ENSO transition
Four El Nino &
Two La Nina
110-yr Ctrl simulation
Shade: SST Counter: zonal wind
7 member ensemble (LAF), 18 mon forecasts: 1st October0 ~the end of April+2