Coupled ocean–atmosphere dynamics in the Indian Ocean during 1997–98

Climate variability in the Indian Ocean region seems to be, in some aspects, independent of forcing by external phenomena such as the El Niño/Southern Oscillation. But the extent to which, and how, internal coupled ocean–atmosphere dynamics determine the state of the Indian Ocean system have not been resolved. Here we present a detailed analysis of the strong seasonal anomalies in sea surface temperatures, sea surface heights, precipitation and winds that occurred in the Indian Ocean region in 1997–98, and compare the results with the record of Indian Ocean climate variability over the past 40 years. We conclude that the 1997–98 anomalies—in spite of the coincidence with the strong El Niño/Southern Oscillation event—may primarily be an expression of internal dynamics, rather than a direct response to external influences. We propose a mechanism of ocean–atmosphere interaction governing the 1997–98 event that may represent a characteristic internal mode of the Indian Ocean climate system. In the Pacific Ocean, the identification of such a mode has led to successful predictions of El Niño; if the proposed Indian Ocean internal mode proves to be robust, there may be a similar potential for predictability of climate in the Indian Ocean region.