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The Indian Ocean Dipole in CMIP5 Models
Weller, E. and Cai, W. 2013. Realism of the Indian Ocean Dipole in CMIP5 models: The implications for climate projections. Journal of Climate 26: 6649-6659.

The authors note that "variability in the Indian Ocean, important for understanding climate on the inter-annual time scale for many surrounding countries, has become an active topic of research in recent decades," citing Schott et al. (2009). And they state in this regard that "previous studies focusing on the performance of models in phase 3 of the Coupled Model Intercomparison Project (CMIP3) have shown that large diversity exists in the IOD [Indian Ocean dipole] strength (Saji et al., 2006; Cai et al., 2011), dynamical and thermodynamical feedbacks (Liu et al., 2011), coherence with ENSO (Saji et al., 2006), and its local and remote rainfall teleconnections (Cai et al., 2009, 2011)."

What was done
In light of these several significant shortcomings, Weller and Cai decided to assess how well 20 different climate models that had taken part in phase 5 of the Coupled Model Intercomparison Project (CMIP5) perform when simulating the IOD.

What was learned
The two Australian researchers report that (1) "compared with models in phase 3 (CMIP3), no substantial improvement is evident in the simulation of the IOD pattern and/or amplitude during austral spring [September-November (SON)]," that (2) "the majority of models in CMIP5 generate a larger variance of sea surface temperature (SST) in the Sumatra-Java upwelling region and an IOD amplitude that is far greater than is observed," that (3) "the diversity of the simulated IOD amplitudes in models in CMIP5 (and CMIP 3), which tend to be overly large, results in a wide range of future modeled SON rainfall trends over IOD-influenced regions," and that (4) "most models in CMIP5 and CMIP3 generate an IOD that is too strong relative to observations."

What it means
Weller and Cai conclude that their results "highlight the importance of realistically simulating the present-day IOD properties and suggest that caution should be exercised in interpreting climate projections in the IOD-affected regions." And by inference, they thus imply that climate models still have a considerable way to go before they can adequately do what people in lands impacted by the Indian Ocean wish they could do.

Cai, W., Sullivan, A. and Cowan, T. 2009. Rainfall teleconnections with Indo-Pacific variability in the WCRP CMIP3 models. Journal of Climate 22: 5046-5071.

Cai, W., Sullivan, A., Cowan, T., Ribbe and Shi, G. 2011. Simulation of the Indian Ocean dipole: A relevant criterion for selecting models for climate projections. Geophysical Research Letters 38: 10.1029/2010GL046242.

Liu, L., Yu, W. and Li, T. 2011. Dynamic and thermodynamic air-sea coupling associated with the Indian Ocean dipole diagnosed from 23 WCRP CMIP3 models. Journal of Climate 24: 4941-4958.

Saji, N.H., Xie, S.-P. and Yamagata, T. 2006. Tropical Indian Ocean variability in the IPCC twentieth-century climate simulations. Journal of Climate 19: 4397-4417.

Schott, F.A., Xie, S.-P. and McCreary Jr., J.P. 2009. Indian Ocean circulation and climate variability. Reviews of Geophysics 47: 10.1029/2007RG000245.

Reviewed 27 November 2013