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.ENSO is a trigger of the IOD, and the IOD can trigger an ENSO event. 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 response If mode A is a forcing of mode B then, A “necessary condition” test (e.g., Cai et al. 2009, 2010) x x x x xx x x x x x x x x x x x x x x Amplitude of mode A Cor, Mode A & Mode 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 Cor., SON SAM & SON IOD

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

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.