Indian Ocean Dipole and ENSO Teleconnections in CMIP5 Models
Weller, E. and Cai, W. 2013. Asymmetry in the IOD and ENSO teleconnections in a CMIP5 model ensemble and its relevance to regional rainfall. Journal of Climate 26: 5139-5149.
Although the models got some things right, they got other things wrong. The two Australian researchers report, for example, that (1) "the asymmetry in the impact of the IOD is distorted by two factors," which are that (2) "the tropical and extratropical response to La Niña is situated unrealistically too far westward," and that (3) it is thus "too close to Australia," leading to (4) "an overly strong impact on southeast Australia." They also note that (5) "the majority of models simulate a positive SST [sea surface temperature] skewness in the eastern Pacific that is too weak," which leads to their (6) "overestimating the impact of La Niña relative to that of El Niño," and that (7) "low model resolution may help generate a pan-Australia rainfall effect exacerbating the tropical bias."
In the closing words of the authors, "most models simulate a slower warming rate in the eastern tropical Indian Ocean than in the western tropical Indian Ocean, inducing a positive IOD-like mean state change, in terms of zonal SST gradients." They also say, "given that the mean state change will influence mean rainfall trends, rainfall projections are likely to be distorted by the biases in the Pacific as well, making it harder for the rainfall trends to emerge." And they thus conclude by noting their results highlight "the importance of reducing the distortion in future projections of rainfall changes in IOD-affected regions such as Australia."