Indian Ocean Dipole and Its Impact on Indian Monsoon

Indian Ocean Dipole (IOD) also known as Indian Nino is an irregular oscillation of sea-surface temperature, in which the Western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.

Positive IOD

During the Positive IOD, the eastern equatorial Indian Ocean off Sumatra in Indonesia becomes colder than normal while the western tropical part of the Indian Ocean near the African coast becomes unusually warm. Such an event has been found to be beneficial for the monsoon.

Negative IOD

In this case the opposite of the above mentioned case occurs. The eastern equatorial Indian Ocean off Sumatra in Indonesia becomes abnormally warm while the western tropical part of the ocean near the African coast becomes relatively colder. This effect obstructs the progression of monsoon over India.

Interplay between IOD and El Nino on Indian Monsoon

Indian monsoon depends upon not only El Nino La Nina but also IOD and other such ocean phenomena. As mentioned above, an IOD can either aggravate or weaken the impact of El Nino on Indian monsoon. If there is a positive IOD, it can bring good rains to India despite of an El Nino year. For example, positive IOD had facilitated normal or excess rainfall over India in 1983, 1994 and 1997 despite an El Nino in those years. Similarly, during years such as 1992, a negative IOD and El Nino had cooperatively produced deficient rainfall.

The positive IOD in 2007 appeared together with La Niña which is a very rare phenomenon that has happened only once in the available historical data (in 1967).