October 22, 2025

IOD and ENSO

  • 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.
  • IOD is defined by the difference in sea surface temperature between the eastern and western sides of the Indian Ocean.
    • The IOD was identified as an independent system in 1999.

RELATION BETWEEN EL NIÑO-SOUTHERN OSCILLATION (ENSO) AND IOD

  • The air circulation in the Indian Ocean is from west to east, and in opposite directions at the upper level.
  • In a normal year warm water from the west Pacific cross over to the Indian Ocean and make the air rise and strengthening the air circulation.
  • During EL nino, the western side of the Pacific is cooler than normal because of which the Indian Ocean side also gets cooler and helps in the development of positive IOD.
  • Similarly negative IOD is associated with LA-Nina.
  • Researchers believe that while external factors such as ENSO can trigger IOD, many times is caused by the local circulations.
  • A positive IOD helps rainfall along the African coast, and Indian subcontinent while suppressing it in the eastern Indian Ocean, and the opposite happens during a negative IOD.
  • The impact of IODs is much weaker as compared to ENSO but they can subdue the impact of ENSO.
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