DEFINITION

A climatic phenomenon was discovered in 1999 by Dr. Toshio Yamagata (Director of climate variations research program, University of Tokyo), Dr. Saji Hameed and other staff and named the IOD (Indian Ocean Dipole). Little is currently know about the IOD. This climatic variation has significant impacts on climate of India and the countries in the neighbourhood following the surface temperature anomalies in the Indian Ocean.

The Indian Ocean Dipole is a phenomenon of interaction between the ocean and the atmosphere in the Indian Ocean. It would be independent of ENSO as only 35% of Indian Ocean Dipole events occur with the ENSO. More in 1961, an IOD+ occurred without El Niño in the Pacific and in 1967, an IOD+ coincided with the Niña and the positive dipole 1997 occurred with a strong El Niño.

The index of the Indian Ocean Dipole is positive when the Indian Ocean sea surface temperature is warmer than the normal to the West and below than the normal in the East.

When there is an IOD+ then in the Western-central tropical Indian Ocean the rainfall totals are higher than normal and then in Eastern Indian Ocean and in western tropical Pacific the rainfall totals are below normal.

Schema of the SST anomalies (in red the SST is warming and in blue it is cooling)
during a positive event of the Indian Ocean Dipole. White spots indicate
activity cloudy and rainy. The arrows indicate the direction of the wind.

The index of Indian Ocean Dipole is negative when the Indian Ocean sea surface temperature is colder than normal in the West and warmer than normal in the East.

With the IOD- then in the western-central tropical Indian Ocean the rainfall totals are lower than normal, while in the eastern tropical Indian Ocean and western tropical Pacific rainfall totals are higher than normal.

Schema of the SST anomalies (in red the SST is warming and in blue it is cooling)
during a negative event of the Indian Ocean Dipole. White spots indicate
activity cloudy and rainy. The arrows indicate the direction of the wind.

INDEX of IOD or DMI

The Indian Ocean Dipole index is named DMI in English. It is according to the difference between the sea surface temperature anomaly of the West (50°E to 70°E and 10°S to 10°N) and Eastern (90°E to 110°E and 10°S to 0°N) of the Indian ocean at the level of Equador that the intensity of the Indian Ocean Dipole is represented and its index is calculated.

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