A dipole mode in the tropical Indian Ocean

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Abstract

For the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized1,2, but in the Indian Ocean region a similar ocean–atmosphere interaction causing interannual climate variability has not yet been found3. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air–sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Niño/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean—and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia—brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries.

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Figure 1: Dipole mode and El Niño events since 1958.
Figure 2: A composite dipole mode event.
Figure 3: Strong coupling of SST dipole intensity to Ueq.
Figure 4: Rainfall shifts northwest of the OTCZ during dipole mode events.

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Acknowledgements

We thank H. Nakamura, Y. Masumoto, S. Behera and Y. Tanimoto for comments and discussions, and H. Watanabe and M. Yoshinaga for assistance in plotting the data.

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Correspondence to T. Yamagata.

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Saji, N., Goswami, B., Vinayachandran, P. et al. A dipole mode in the tropical Indian Ocean. Nature 401, 360–363 (1999) doi:10.1038/43854

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