Question 86 from UPSC CSE 2017 - Geography

Question

With reference to 'Indian Ocean Dipole (IOD)' sometimes mentioned in the news while forecasting the Indian monsoon, which of the following statements is/are correct?
1. IOD phenomenon is characterised by a difference in sea surface temperature between the tropical Western Indian Ocean and the tropical Eastern Indian Ocean.
2. An IOD phenomenon can influence an El NiÃ±o's impact on the monsoon.
Select the correct answer using the code given below:

IASCODEX · Accepted Answer

Correct Option: B. 2 only

Strategy: Select the second statement as it accurately describes the IOD's influence on the Indian Monsoon. Reject the first statement because it contains a subtle inaccuracy; the IOD specifically concerns the sea surface temperature difference between the western and eastern equatorial Indian Ocean, not just the broader tropical regions. Precision in scientific definitions is key.

Key Info: ## Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere phenomenon in the Indian Ocean, characterized by a seesaw in sea surface temperatures (SST) between the western equatorial Indian Ocean (off the African coast) and the eastern equatorial Indian Ocean (near Indonesia and Australia).

A positive IOD event features warmer SSTs in the west and cooler SSTs in the east, altering atmospheric circulation. While distinct from El Niño-Southern Oscillation (ENSO), the IOD can interact with it. During an El Niño event, the Indian monsoon typically weakens, but a strong positive IOD can mitigate or even reverse this negative impact, leading to normal or above-normal rainfall in India.

The IOD is measured using the Dipole Mode Index (DMI), which calculates the SST gradient between two specific regions: the western pole (50°E–70°E, 10°S–10°N) and the eastern pole (90°E–110°E, 10°S–0°N).

The IOD has significant implications for rainfall variability across several regions, including:
- East Africa, Indonesia, Australia, and the Indian subcontinent.
- Positive and negative IOD phases correspondingly affect flooding and drought patterns in these areas.

Key research institutions involved in IOD and monsoon research include the Indian Institute of Tropical Meteorology (IITM) and the Indian Meteorological Department (IMD).

IASCODEX · Answer

Option A: 1 only

IASCODEX · Answer

Option C: Both 1 and 2

IASCODEX · Answer

Option D: Neither 1 nor 2