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Relationship between large-scale climate drivers: the SAM, the IOD, & ENSO). Wenju Cai and Tim Cowan (Australia) Cai, W., A. Sullivan, and T. Cowan (2010) , Interactions of ENSO, the IOD, and the SAM in CMIP3 models, J. Climate, conditionally accepted . - PowerPoint PPT Presentation
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Relationship between large-scale climate drivers: the SAM, the IOD, & ENSO)
Wenju Cai and Tim Cowan (Australia)
Cai, W., A. Sullivan, and T. Cowan (2010), Interactions of ENSO, the IOD, and the SAM in CMIP3 models, J. Climate, conditionally accepted.
Cai, W., A. Sullivan, and T. Cowan (2009), Rainfall Teleconnections with Indo-Pacific Variability in the WCRP CMIP3 Models. J. Climate, 22, 5046–5071.
CSIRO. Statistical Climatology
Cerberus
ENSO
Cerberus
ENSO
Three-headed dog of the Australian climate
Southern Annular ModeSouthern Annular Mode: SAM
Indian Ocean Dipole: IOD
CSIRO. Statistical Climatology
We know that ENSO is a trigger of the IOD, and the IOD can trigger an ENSO event. The community knows the associated processes.
A previous study suggests that the SAM can force an IOD. Is it likely?
Multi-model statistics can help! (up to 24 models)
The relationship of the three heads of the dog
Useful.
No.
CSIRO. Statistical Climatology
Multi-model: forcing and responseIf mode A is a forcing of mode B then,
A “necessary condition” test (e.g., Cai et al. 2009, 2010)
xx
xx
xx xx
x
x
x
xx xx
x
x
xx
x
Amplitude of mode A
Co
r, M
od
e A
&
Mo
de
B
If this condition is met, it is not sufficient, a process linking them must be identified. If this condition is not met, mode A is unlikely a forcing of mode B.
CSIRO. Statistical Climatology
Greater than 0.42 (significant at the 95% confidence level)
ENSO is a forcing of the IOD, and the IOD can trigger an ENSO event
CSIRO. Statistical Climatology
Lau and Nath (2004) show that in the GFDL model, for weak ENSO years …
Composite pIOD – nIOD: contour MSLP; colour, rainfall
JJA SON
They take a time series of MSLP in the AUS region and regress winds, MSLP, and SST onto the time series.
The IOD peaks in SON, therefore the AUS MSLP leads the IOD.
The associated circulation pattern is SAM-like ! The inference is that the SAM forces the IOD.
CSIRO. Statistical Climatology
NCEP (“observed”) direct correlation between the SAM & SST shows no IOD pattern.
CSIRO. Statistical Climatology
Does the SAM force the IOD ?
SON SAM standard deviation
Co
r., S
ON
SA
M &
SO
N IO
D
CSIRO. Statistical Climatology
JJA SAM has no impact on SON IOD
CSIRO. Statistical Climatology
It turns out that…
Composite pIOD – nIOD: contour MSLP; colour, rainfall
JJA SON
CSIRO. Statistical Climatology
Tropical SST acts to trigger convection anomalies, thereby generating anomalous vertical motion: anomalous divergence acts as a Rossby wave source.
Response is baroclinic confined in the tropics (e.g., Gill, 1980), and steady equivalent-barotropic wavetrain pattern in extratropics (e.g., Hoskins and Karoly, 1980)
Tropical and extra-tropical responses to IOD-induced convection anomalies
JJA SST a/w the IOD JJA OLR a/w the IOD
CSIRO. Statistical Climatology
Equivalent barotropic wavetrain pattern
MSLP 200mb Australian rainfall
CSIRO. Statistical Climatology
Using the “necessary condition” to select models for climate projection
CSIRO. Statistical Climatology
CSIRO. Statistical Climatology
Pre-industrial range of 100yr spectra of ENSO
Even if a model is perfect we are going to see substantial differences in results depending on where 100-yr output is in.
Not too hang up with the performance of individual model but use the statistics of all models.
