Role of Indian Ocean Dipole (IOD)

It is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia. Due to apparent changes in the thermal and atmospheric conditions of Tropical Indian Ocean, this is also known as ‘Indian Nino’.

It is of two types: positive IOD and negative IOD. It affects Indian summer monsoon rainfall. A positive IOD occurs when the sea surface temperatures are greater than normal in the Arabian Sea and less than normal in the tropical eastern Indian Ocean. When the reverse is the case, a negative IOD is said to have developed.

A positive IOD leads to greater monsoon rainfall and more active (above normal rainfall) monsoon days in Indian sub-continent while negative IOD leads to less rainfall and more monsoon break days (no rainfall).

Indian Monsoon