Indian Ocean Dipole – UPSC Prelims

The Indian Ocean Dipole (IOD) 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.

IOD develops in the equatorial region of Indian Ocean from April to May peaking in October.

With a positive IOD winds over the Indian Ocean blow from east to west (from Bay of Bengal towards Arabian Sea). This results in the Arabian Sea (western Indian Ocean near African Coast) being much warmer and eastern Indian Ocean around Indonesia becoming colder and dry.

In the negative dipole year (negative IOD), reverse happens making Indonesia much warmer and rainier.

It was demonstrated that a positive IOD index often negated the effect of El Nino, resulting in increased Monsoon rains in several El Nino years like the 1983, 1994 and 1997.

Two poles of the IOD – the eastern pole (around Indonesia) and the western pole (off the African coast) were independently and cumulatively affecting the quantity of rains for the Monsoon in the Indian subcontinent.

Positive IOD (Arabian Sea warmer than Bay of Bengal) results in more cyclones than usual in Arabian Sea.

Negative IOD results in stronger than usual Tropical Cyclones in the Bay of Bengal. Cyclonic activity in Arabian Sea is suppressed.