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Proper Modeling of the Seychelles Dome: Is Progress Being Made?

Nagura, M., Sasaki, W., Tozuka, T., Luo, J.-J., Behera, S.K. and Yamagata, T. 2013. Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models. Journal of Geophysical Research: Oceans 118: 831-846.
In the words of Nagura et al. (2013), "the Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, where ocean wave dynamics efficiently affect sea surface temperature, allowing sea surface temperature anomalies to be predicted up to 1-2 years in advance." And they note, in this regard, that "accurate reproduction of the dome by ocean-atmosphere coupled general circulation models (CGCMs) is essential for successful seasonal predictions in the Indian Ocean."

Resolved to determine if CGCMs are doing their job in this situation, Nagura et al. examined the Seychelles Dome as it has been simulated by 35 different CGCMs, including models used in phase five of the Coupled Model Intercomparison Project (CMIP5). Quoting the six scientists, they find that "among the 35 CGCMs, 14 models erroneously produce an upwelling dome in the eastern half of the basin whereas the observed Seychelles Dome is located in the southwestern tropical Indian Ocean." In addition, they report that "the annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region," which finding, as they describe it, "is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome."

In an earlier study, Yokoi et al. (2009) had examined the outputs from models used in phase three of the Coupled Model Intercomparison Project (CMIP3), finding, in Nagura et al.'s words, that "many CMIP3 models have serious biases in this region." But when all was said and done, the sad conclusion of Nagura et al. was that "compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes." Could we call this state of affairs retro-progress???

Additional References
Yokoi, T., Tozuka, T. and Yamagata, T. 2009. Seasonal variations of the Seychelles Dome simulated in the CMIP3 models. Journal of Climate 39: 449-457.

Archived 21 August 2013