Indian Ocean Dipole

Indian Ocean Dipole

  • Indian Ocean Dipole (IOD) is sometimes also referred to as the Indian Niño due to its similarity with the El Niño.
  • Indian Ocean Dipole the difference in sea surface temperature between two areas i.e., the Arabian Sea in the west and Bay of Bengal till south of Indonesia in the east.
  • In technical terms, the IOD is a coupled ocean and atmosphere phenomenon, similar to El Niño but in the equatorial Indian Ocean.
  • IOD is believed to be linked with ENSO through an extension of the Walker Circulation to the west and the flow of warm tropical ocean water from the Pacific into the Indian Ocean.
  • Therefore, positive IOD events are often associated with El Niño and negative events with La Niña.
  • The strength of the IOD is measured using the Dipole Mode Index.

Positive IOD

  • The dipole’s positive phase denotes warmer sea temperatures in the western Indian Ocean region (Arabian Sea), with the opposite in the east (Bay of Bengal).
  • The positive phase of IOD typically peaks in the months of September till November.
  • Positive IOD can result in floods in eastern Africa and droughts and bushfires in eastern Asia and Australia.
  • At the same time, Positive IOD increases the chance of formation of cyclones (cyclogenesis) in the Arabian Sea.
  • Monsoon rainfall has been known increases during positive IOD due to increased temperature in the Arabian Sea region.
  • However, a positive IOD does not automatically translate into higher monsoon rainfall as monsoon is influenced by a number of factors.

Negative IOD

  • Negative IOD represents a cooler sea surface temperatures in the western Indian Ocean (Arabian Sea) relative to the east (Bay of Bengal).
  • This causes Indonesia and Australia to be wetter than normal, while making eastern Africa to be drier than normal.
  • Negative IOD increases the chance of formation of cyclones (cyclogenesis) in the Bay of Bengal.
  • A negative IOD in tandem with El Nino can cause severe drought.

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