Prelims 2017 · Q66
MediumWith 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:
Answer & explanation
Answer: (b) 2 only
The Indian Ocean Dipole is a sea-surface temperature difference between the western and the south-eastern tropical Indian Ocean, not the Eastern Pacific, so statement 1 is wrong. A positive or negative IOD can strengthen or weaken the effect of an El Nino on the Indian monsoon, so statement 2 is correct.
- ✗ 1. The IOD is measured as the temperature difference between the tropical western Indian Ocean and the tropical south-eastern Indian Ocean. The Eastern Pacific is the region watched for El Nino and La Nina, which is a different phenomenon.
- ✓ 2. The El Nino-induced circulation over India can be countered or supported by the circulation the IOD sets up, depending on the phase and strength of each. This is why a positive IOD can soften an El Nino's damage to the monsoon.
Remember · IOD = west-minus-east sea-surface temperature contrast inside the Indian Ocean. It can counter or reinforce El Nino's effect on the Indian monsoon.
Sources
- India Meteorological Department, MAUSAM 72(4), 2021: Indian Ocean Dipole: assessing its impacts on the Indian Summer Monsoon Rainfall across North East India ↗ “The Indian Ocean Dipole (IOD), a climatic anomaly, results in sustained sea surface temperature (SST) variations between tropical western and eastern Indian Ocean temperatures.”
- Ashok, Guan and Yamagata (2001), Geophysical Research Letters: Impact of the Indian Ocean Dipole on the Relationship between the Indian Monsoon Rainfall and ENSO (JAMSTEC copy) ↗ · reference work “An index to quantify the IOD has been defined [Saji et al., 1999] as the SST difference between the tropical western Indian Ocean (50oE-70oE, 10oS-10oN) and the tropical southeastern Indian Ocean … the ENSO-induced anomalous circulation over the Indian region is either countered or supported by the IOD-induced anomalous meridional circulation cell”
- Ministry of Earth Sciences, Lok Sabha reply on El Nino ↗ “Historically, El Niño has been associated with weaker Indian Summer Monsoon rainfall over parts of the country, although the monsoon is also influenced by other climate drivers such as the Indian Ocean Dipole (IOD)”
Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·