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Relationship between large-scale climate drivers: the SAM, the IOD, & ENSO)

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 .

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Relationship between large-scale climate drivers: the SAM, the IOD, & ENSO)

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  1. 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.

  2. Indian Ocean Dipole: IOD ENSO ENSO Cerberus Cerberus Southern Annular Mode Southern Annular Mode: SAM Three-headed dog of the Australian climate CSIRO. Statistical Climatology

  3. The relationship of the three heads of the dog 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) No. • Useful. CSIRO. Statistical Climatology

  4. x x x x x x x x x x x x Cor, Mode A & Mode B x x x x x x x Amplitude of mode A 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) x 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

  5. ENSO is a forcing of the IOD, and the IOD can trigger an ENSO event Greater than 0.42 (significant at the 95% confidence level) CSIRO. Statistical Climatology

  6. Composite pIOD – nIOD: contour MSLP; colour, rainfall JJA SON Lau and Nath (2004) show that in the GFDL model, for weak ENSO years … The IOD peaks in SON, therefore the AUS MSLP leads the IOD. They take a time series of MSLP in the AUS region and regress winds, MSLP, and SST onto the time series. The associated circulation pattern is SAM-like ! The inference is that the SAM forces the IOD. CSIRO. Statistical Climatology

  7. NCEP (“observed”) direct correlation between the SAM & SST shows no IOD pattern. CSIRO. Statistical Climatology

  8. Does the SAM force the IOD ? Cor., SON SAM & SON IOD SON SAM standard deviation CSIRO. Statistical Climatology

  9. JJA SAM has no impact on SON IOD CSIRO. Statistical Climatology

  10. Composite pIOD – nIOD: contour MSLP; colour, rainfall JJA SON It turns out that… CSIRO. Statistical Climatology

  11. JJA SST a/w the IOD JJA OLR a/w the IOD Tropical and extra-tropical responses to IOD-induced convection anomalies 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) CSIRO. Statistical Climatology

  12. Equivalent barotropic wavetrain pattern Australian rainfall MSLP 200mb CSIRO. Statistical Climatology

  13. Using the “necessary condition” to select models for climate projection CSIRO. Statistical Climatology

  14. CSIRO. Statistical Climatology

  15. 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. CSIRO. Statistical Climatology

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