Indian Ocean Dipole: What is it, how it can limit El Nino effects
Context- With the El Nino phenomenon almost certain to affect the Indian monsoon this year, high hopes are pinned on the development of a positive Indian Ocean Dipole (IOD) and its ability to counterbalance the El Nino effect. The IOD is an ocean-atmosphere interaction very similar to the El Nino fluctuations in the Pacific Ocean, playing out, as the name shows, in the Indian Ocean. It is also a much weaker system than El Nino, and thus has relatively limited impacts.
(Credits- EGU Blogs)
But a positive IOD does have the potential to offset the impacts of El Nino to a small measure in neighbouring areas, and it has, at least once in the past (1997), delivered admirably on this potential.
The India Meteorological Department (IMD), in its bulletin earlier this month, said there was an 80% chance of a positive IOD in the coming months.
The Indian Nino
- In a normal year, the eastern side of the Pacific Ocean, near the northwestern coast of South America, is cooler than the western side near the islands of Philippines and Indonesia. This happens because the prevailing wind systems that move from east to west sweep the warmer surface waters towards the Indonesian coast.
- The relatively cooler waters from below come up to replace the displaced water. An El Nino event is the result of a weakening of wind systems that leads to lesser displacement of warmer waters. This results in the eastern side of the Pacific becoming warmer than usual. During La Nina, the opposite happens.
- Both these conditions, together called El Nino Southern Oscillation or ENSO, affect weather events across the world. Over India, the El Nino has the impact of suppressing monsoon rainfall.
- IOD, sometimes referred to as the Indian Nino, is a similar phenomenon, playing out in the relatively smaller area of the Indian Ocean between the Indonesian and Malaysian coastline in the east and the African coastline near Somalia in the west.
- One side of the ocean, along the equator, gets warmer than the other. IOD is said to be positive when the western side of the Indian Ocean. It is negative when the western Indian Ocean is cooler.
ENSO and IOD
- A positive IOD event is often seen developing at times of an El Nino, while a negative IOD is sometimes associated with La Nina.
- During El Nino, the Pacific side of Indonesia is cooler than normal because of which the Indian Ocean side also gets cooler. That helps the development of a positive IOD.
IOD impacts
- A positive IOD helps rainfall along the African coastline and also over the Indian sub-continent while suppressing rainfall over Indonesia, southeast Asia and Australia. The impacts are opposite during a negative IOD event.
- Compared to ENSO events, the impacts of IODs are much weaker. But hope lingers, including this year when a strong El Nino is expected to develop in the Pacific Ocean.
Conclusion- The Indian Ocean Dipole (IOD) is an ocean-atmosphere interaction very similar to the El Nino fluctuations in the Pacific Ocean. In an El nino year IOD can help lessen the impact of monsoon deficit of Rainfall.
Syllabus- GS-1; Geography
Source- Indian Express
