A positive Indian Ocean Dipole (IOD) plus El Niño

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A positive Indian Ocean Dipole (IOD) plus El Niño 

A recent report from the Australian Bureau of Meteorology states that the IOD index has moved beyond the positive range.

Indian Ocean Dipole (IOD):

  • The IOD is the difference in sea surface temperature between the Western Indian Ocean and the Eastern Indian Ocean that affects the monsoon in India. Hence, it is called a dipole. It is also called ‘Indian Nino’.
  • A positive IOD event, which is characterized by warm temperatures in the western basin, can enhance India’s southwest monsoon.

Two phases of the Indian Ocean Dipole:

  • Positive IOD: This occurs when the western part of the Indian Ocean (near the Somalia coast) becomes warmer than the eastern Indian Ocean. A positive IOD is believed to favor rainfall over the Indian subcontinent and the African coast, while reducing the chance of rainfall over Indonesia, Southeast Asia, and Australia.
  • Negative IOD: On the other hand, the cooling of the western Indian Ocean and the warming of the eastern Indian Ocean lead to negative IOD conditions. As a result, Australia receives more rainfall, while East Africa experiences dry conditions. But when the temperature is close to normal over the entire Indian Ocean, the situation is called neutral IOD.

IOD’s relationship to the El Nino/La Nina Southern Oscillation (ENSO)

  • The IOD is associated with the El Nino/La Nina Southern Oscillation (ENSO). This association is manifested through the extension of the Walker Circulation to the west and associated warm water flow from the Pacific Ocean to the Indian Ocean. Be aware that ‘Walker Circulation’ is the flow of air in the equatorial Pacific region.
  • Positive IOD phenomena are commonly associated with El-Nino, an abnormal increase in the temperature of the equatorial Pacific Ocean.
  • While the phenomenon of negative IOD is associated with La-Nina. Abnormal cooling conditions are observed by this.

Source – The Hindu

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