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Simulating the Southwestern Indian Ocean's Seychelles Dome

Reference
Nagura, M., Sasaki, W., Tozuka, T., Luo, J.-J., Behera, S. 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: 1-16.
Writing as background for their work, Nagura et al. (2013) state that the term Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, "where ocean wave dynamics efficiently affect sea surface temperature [SST], allowing SST anomalies to be predicted up to 1-2 years in advance." They then indicate that this ability is quite significant; for they note that "the anomalous SSTs in the dome region subsequently impact various atmospheric phenomena, such as tropical cyclones (Xie et al., 2002), the onset of the Indian summer monsoon (Joseph et al., 1994; Annamalai et al., 2005) and precipitation over India and Africa (Annamalai et al., 2007; Izumo et al., 2008)." And as further background for their work, they report that "Yokoi et al. (2009) examined the outputs from models used in phase three of the Coupled Model Intercomparison Project (CMIP3) and found that many CMIP3 models have serious biases in this region."

Hoping to find some improvement in this regard over the following four years, Nagura et al. (2013) examined model biases associated with the Scychelles Dome using state-of-the-art ocean-atmosphere coupled general circulation models (CGCMs), "including those from phase five of the Coupled Model Intercomparison Project (CMIP5)." In doing so, the six scientists report that (1) several of the tested 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," that (2) "the annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region," which "is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome," and that (3) "in the models reproducing an eastward-displaced dome, easterly biases are prominent along the equator in boreal summer and fall, which result in shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and a spurious upwelling dome in the region."

In a revealing final assessment of their findings, Nagura et al. conclude that "compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes." So in a slight departure from what has become somewhat of a recurring theme in reviewing CMIP3 vs. CMIP5 models, it appears that the new models are even worse than the old ones.

Additional References
Annamalai, H., Liu, P. and Xie, S.-P. 2005. Southwest Indian Ocean SST variability: Its local effect and remote influence on Asian monsoons. Journal of Climate 18: 4150-4167.

Annamalai, H., Okajima, H. and Watanabe, M. 2007. Possible impact of the Indian Ocean SST on the Northern Hemisphere circulation during El Niņo. Journal of Climate 20: 3164-3189.

Izumo, T., Montegut, C.D.B., Luo, J.-J., Behera, S.K., Masson, S. and Yamagata, T. 2008. The role of the western Arabian Sea upwelling in Indian Monsoon rainfall variability. Journal of Climate 21: 5603-5623.

Joseph, P.V., Eischeid, J.K. and Pyle, R.J. 1994. Interannual variability of the onset of the Indian summer monsoon and its association with atmospheric features, El Niņo, and sea surface temperature anomalies. Journal of Climate 7: 81-105.

Xie, S.-P., Annamalai, H., Schott, F.A. and McCreary Jr., J.P. 2002. Structure and mechanisms of south Indian Ocean climate variability. Journal of Climate 15: 864-878.

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 5 June 2013