UPSC Prelims 2017 Q66: Geography – Atmosphere & Climatology
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 Niño’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
Answer: (b) 2 only
Explanation
Indian Ocean Dipole (IOD)
The IOD is a see-saw of sea surface temperature within the Indian Ocean.
| Statement | Verdict | Fact |
|---|---|---|
| 1. IOD is a difference in sea surface temperature between the tropical Western Indian Ocean and the tropical Eastern Pacific Ocean | Incorrect | The difference is between the western and eastern Indian Ocean; the Pacific is not involved |
| 2. An IOD phenomenon can influence an El Nino's impact on the monsoon | Correct | A positive IOD can offset the drying effect of El Nino, as in 1997 |
Phases of the IOD:
| Phase | Warmer side | Effect on Indian monsoon |
|---|---|---|
| Positive | Western Indian Ocean (Arabian Sea side) | Good rainfall |
| Negative | Eastern Indian Ocean (near Indonesia) | Weaker rainfall |
The IOD is also called the Indian Nino.
Answer: (b) 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false; the IOD compares two parts of the Indian Ocean only.
- (b) CORRECT. The IOD can influence El Nino's impact on the Indian monsoon.
- (c) Incorrect. Statement 1 wrongly brings in the Eastern Pacific Ocean.
- (d) Incorrect. Statement 2 is true; a positive IOD can cancel El Nino's effect.
Key point
IOD = temperature difference between western and eastern Indian Ocean; positive IOD (warm west) helps the monsoon and can offset El Nino.
Remember
Positive IOD = warm western Indian Ocean = good monsoon.
Common mistakes
- Missing the swap of Eastern Indian Ocean with Eastern Pacific Ocean in statement 1.
- Thinking El Nino always means drought in India; a positive IOD can save the monsoon.
- Reversing the phases: positive means the western side is warmer.
Exam tip
Indian Ocean Dipole stays inside the Indian Ocean. If the Pacific appears in its definition, it is wrong.
Sources
- India Meteorological Department — Monsoon FAQs: Indian Ocean Dipole
- NCERT Class XI — India: Physical Environment, Ch 4 (Climate)