The Indian Ocean Dipole (IOD) is defined by the difference in the sea surface temperature between the two equatorial areas of the Indian Ocean – a western pole near the Arabian Sea (in western Indian Ocean) and an eastern pole closer to the Bay of Bengal (in eastern Indian Ocean). The IOD affects the climate of Southeast Asia, Australia and other countries that surround the Indian Ocean Basin. The Indian Monsoon is invariably influenced by the IOD.
IOD is simply the periodic oscillation of sea surface temperatures, from ‘positive’ to ‘neutral’ and then ‘negative’ phases. If the sea surface temperature of the western end rises above normal (0.4°C) and becomes warmer than the eastern end, it leads to a positive IOD. This condition is favourable for the Indian Monsoon as it causes a kind of barrier in the eastern Indian Ocean and all the southwesterly winds blow towards the Indian sub-continent.
Accordingly, the waters in the eastern Indian Ocean cools down, which tends to cause droughts in adjacent land areas of Indonesia and Australia.
Conversely, during a negative IOD period the waters of the tropical eastern Indian Ocean is warmer than water in the tropical western Indian Ocean. This results in increased rainfall over parts of southern Australia.
Difference between El Nino and IOD
The Indian Ocean Dipole (IOD) and the El Nino are independent climatic phenomena but often co-occur. Both IOD and El Nino result in change of global wind patterns. To know about the change of wind patterns, click here.
However the cycle of IOD is shorter, while El Nino condition could last for even two years. IOD commences in the month of May and end with the withdrawal of Southwest Monsoon in the Indian sub-continent.
To know about the Impact of El Nino on Indian Monsoon, click here.
For latest updates on Monsoon 2015, click here.
Image credit - The Hindu
