Indian Ocean Dipole and its Effect on El Nino

Why in news?

Experts have predicted a positive Indian Ocean Dipole in the coming months.

What is Indian Ocean Dipole?

• The Indian Ocean Dipole (IOD) is a coupled ocean ­atmosphere phenomenon in the Indian Ocean.

• IOD is defined by the difference in sea surface temperature between the western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
• What is Indian Ocean Dipole, how it will impact Monsoon this year?
• The IOD is sometimes called India’s El-Nino and its impact can be seen in weather and climate patterns in India and as far as Indonesia, Australia, New Zealand and Africa.

What are the phases of IOD?

• IOD has 3 phases - Positive IOD, Neutral Phase, Negative IOD
• Positive event- Warmer sea surface temperatures in the western Indian Ocean relative to the east.
• It brings more rainfall to India.

• Neutral event-Water flows from the Pacific between Indonesia’s islands, keeping seas warm to the northwest of Australia.
• Air rises above this area and falls across the western half of Indian Ocean basin, blowing westerly winds along the equator.
• This has very less impact of Indian monsoon.

• Negative event- Cooler sea surface temperatures in the western Indian Ocean relative to the east.
• It brings less rainfall to India.

The Indian Ocean Dipole is currently neutral. The India Meteorological Department (IMD) has said that there was an 80% chance of a positive IOD in the coming months.

What is ENSO?

• El Nino - El Nino is the warming of sea waters in Central-east Equatorial Pacific that occurs every few years (Warm phase off the coast of Peru).
• Over India, the El Nino has the impact of suppressing monsoon rainfall.
• La Nina - La Niña sees cooler than average sea surface temperatures in the equatorial Pacific region (Cool phase).
• In the Indian context, La Nina is associated with good rainfall during the monsoon season.
• Both these conditions, together called El Nino Southern Oscillation or ENSO, affect weather events across the world.

To know more about El Niño-La Niña Weather Patterns, click here

What is the effect of IOD on ENSO?

• 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.
• If both IOD and ENSO are strong their circulation can impact each other.
• Compared to ENSO events, the impacts of IODs are much weaker.

Quick facts

India Meteorological Department (IMD)

• IMD was established in 1875.
• It is the national meteorological service of the country and the principal government agency in all matters relating to meteorology and allied subjects.
• It works under the aegis of Ministry of Earth Science.

References

1. The Indian Express | Indian Ocean Dipole
2. The Hindu | Outlook for Monsoon
3. IMD| India Meteorological Department