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  • Saji, N. H., and S.-P. Xie and T. Yamagata, 2005: Tropical Indian Ocean variability in the IPCC 20th-century climate simulations. J. Climate. In press.

The 20th century simulations by 17 coupled ocean-atmosphere general circulation models (CGCMs) submitted to the Intergovernmental Panel for Climate Change Fourth Assessment Report (IPCC AR4) are evaluated for their skills in reproducing the observed modes of Indian Ocean (IO) climate variability. Most models successfully capture the IO’s delayed, basin-wide warming response
a few months after El Nino/Southern Oscillation (ENSO) peaks in the Pacific. ENSO’s oceanic teleconnection into the IO, by coastal waves through the Indonesian archipelago, is poorly simulated in these models, with significant shifts in the turning latitude of radiating Rossby waves. In observations, ENSO forces, by the atmospheric bridge mechanism, strong ocean Rossby waves
that induce anomalies of SST, atmospheric convection and tropical cyclones in a thermocline dome over the southwestern tropical IO. While the southwestern IO thermocline dome is simulated in nearly all the models, this ocean Rossby wave response to ENSO is present only in a few of the models examined, suggesting difficulties in simulating ENSO’s teleconnection in surface wind. A majority of models display an equatorial zonal mode of the Bjerknes feedback with spatial
structures and seasonality similar to the Indian Ocean dipole (IOD) in observations. This success appears due to their skills in simulating the mean state of the equatorial IO. Corroborating the role of the Bjerknes feedback in IOD, the thermocline depth, SST, precipitation and zonal wind are mutually positively correlated in these models, as in observations. The IOD-ENSO correlation during boreal fall ranges from -0.43 to 0.74 in the different models, suggesting that ENSO is one, but not the only, trigger for IOD.

Full Article: http://iprc.soest.hawaii.edu/~saji/cgcm_iovar.pdf

Last Updated: 2006-05-04

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