Global Geological And Climatic Events

Positive Indian Ocean Dipole (IOD) to aid Monsoon this year


From UPSC perspective, the following things are important :

Prelims level: IOD and its phases, ENSO;

Why in the News?

Australian weather agencies predict the possible return of a positive Indian Ocean Dipole (IOD) in the latter half of 2024.

What is the Indian Ocean Dipole (IOD)?

  • The IOD is also known as the Indian Nino. It is characterized by the differential heating of ocean waters in the eastern and western parts of the basin.
  • Similar to the El Nino Southern Oscillation (ENSO) in the Pacific, the IOD involves phases of ocean temperatures and atmospheric conditions that affect weather patterns across the region and beyond.
  • There are two main phases of the IOD:
    • Positive Phase: In this phase, the western Indian Ocean becomes warmer than average, and the eastern part cooler than average. This results in greater convection and rainfall over the western Indian Ocean and adjacent land areas like East Africa, while reducing rainfall over the eastern Indian Ocean and places like Indonesia and Australia.
    • Negative Phase: The opposite conditions prevail during this phase, with cooler waters in the western Indian Ocean and warmer waters in the east. This leads to increased rainfall in the eastern Indian Ocean regions and drier conditions in the western part and East Africa.

Back2Basics: El Nino-Southern Oscillation (ENSO)

  • El Nino and La Nina are two opposite phases of the El Nino-Southern Oscillation (ENSO) cycle.
  • ENSO is a naturally occurring phenomenon that involves the interaction between the ocean and atmosphere in the equatorial Pacific.

Here is a detailed comparison of El Nino and La Nina

El Nino La Nina
Definition Warmer-than-normal sea surface temperatures Cooler-than-normal sea surface temperatures
Frequency Every two to seven years Every two to seven years
Duration Several months to a year or more Several months to a year or more
Impact on winds Weakens trade winds, leading to changes in patterns Strengthens trade winds, leading to changes in patterns
Impact on rains Reduces rainfall and can cause droughts Increases rainfall and can cause flooding
Impact on temp. Warmer-than-average temperatures Colder-than-average temperatures
Global effects Droughts in Asia and Africa, floods in Americas Floods in Asia and Africa, droughts in South America


Impact on the Indian Monsoon:

The Indian Ocean Dipole has significant impacts on the Indian monsoon system:

  1. Positive IOD often coincides with a stronger Southwest Monsoon, bringing more rainfall to India. This is due to the shift in warm water and accompanying convection towards India, which enhances the monsoon rainfall.
  2. Negative IOD can weaken the Southwest Monsoon, resulting in less rainfall and potential drought conditions in India. The shift of warm water away from India reduces the necessary heat and moisture that drive the monsoon rains.


[2017] With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?

1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.

2. An IOD phenomenon can influence an El Nino’s impact on the monsoon.

Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

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