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:

The correct answer is 2 only.

Let us analyze each statement carefully to understand why only Statement 2 is correct.

Statement 1 Analysis — INCORRECT:

Statement 1 claims that the IOD is characterised by a difference in sea surface temperature (SST) between the tropical Western Indian Ocean and the tropical Eastern Pacific Ocean.

This is factually wrong. The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperatures between two regions within the Indian Ocean itself:

• The tropical Western Indian Ocean (near the Arabian Sea coast of East Africa)
• The tropical Eastern Indian Ocean (near the coast of Sumatra/Indonesia)

The Eastern Pacific Ocean is associated with a completely different phenomenon — the El Niño-Southern Oscillation (ENSO), not the IOD. Statement 1 incorrectly replaces "Eastern Indian Ocean" with "Eastern Pacific Ocean," making it factually incorrect.

What exactly is IOD?

The IOD (also called the Indian Niño) is an irregular oscillation of sea surface temperatures where the western Indian Ocean becomes alternately warmer (+ve IOD) or cooler (-ve IOD) than the eastern Indian Ocean.

• Positive IOD (+ve IOD): Western Indian Ocean is warmer than eastern Indian Ocean → generally favourable for Indian monsoon rainfall.
• Negative IOD (-ve IOD): Western Indian Ocean is cooler than eastern Indian Ocean → generally unfavourable for Indian monsoon rainfall.

Statement 2 Analysis — CORRECT:

Statement 2 states that an IOD phenomenon can influence an El Niño's impact on the monsoon.

This is absolutely correct. The IOD and El Niño are two separate but interacting climate phenomena. Historical data and scientific research show that:

• A positive IOD can counteract or neutralise the adverse effects of an El Niño on the Indian monsoon. For instance, during years when El Niño (which typically weakens Indian monsoon) co-occurs with a positive IOD, the monsoon may not be as deficient as expected.
• A negative IOD can compound or worsen the negative effects of El Niño on rainfall.
• Similarly, even in the absence of El Niño, a strongly positive IOD can boost monsoon rainfall, and a negative IOD can suppress it.

This interaction makes the IOD a critical modulator of Indian monsoon variability, and meteorologists and climate scientists now actively track IOD conditions alongside ENSO while forecasting the Indian monsoon season.

Conclusion:

Statement 1 is incorrect because IOD measures the SST difference within the Indian Ocean (western vs. eastern Indian Ocean), not between the Indian Ocean and the Pacific Ocean.
Statement 2 is correct because the IOD does have a well-established modulating influence on El Niño's impact on the Indian monsoon.

Therefore, the correct answer is 2 only.