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UPSC Prelims 2011 · Indian Geography · Monsoon and Climate
La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino? Which of the statements given above is/are correct?
- La Nina is characterized by unusually cold ocean temperatures in the equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperatures in the equatorial Pacific Ocean.
- El Nino has an adverse effect on the southwest monsoon of India, but La Nina has no effect on the monsoon climate.
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Show the answer and explanation
Answer: (d) Neither 1 nor 2
Both are Pacific phenomena, and La Niña usually boosts India’s monsoon.
Statement by statement
1. ✗ WRONG La Niña means unusually cold water in the equatorial PACIFIC, not the Indian Ocean.
2. ✗ WRONG La Niña usually strengthens the Indian monsoon — it does have an effect.
The idea
El Niño and La Niña are opposite phases of a coupled ocean–air pattern in the tropical Pacific. Changes in ocean temperature shift rising air, clouds and the trade winds. These shifts affect distant rainfall, but Indian Ocean conditions can modify their effect on India.
La Niña cooling in the central and eastern Pacific → Pacific trade winds usually strengthen → Warm water gathers towards the western Pacific → Rising air becomes stronger there → Tropical circulation changes → Indian summer monsoon is often favoured
Why the others are wrong
(a) Puts La Niña in the Indian Ocean.
(b) Says La Niña has no effect.
(c) Accepts both errors.
The trap
Statement 1 changes one word — Indian Ocean — to catch you.
Elimination technique
An Indian Ocean location makes statement 1 false, removing (a) and (c). Statement 2 says La Niña has no influence at all; its effect on tropical circulation disproves that claim and removes (b).
Also know
The Southern Oscillation is the air-pressure part of ENSO; its index uses the pressure difference between Tahiti and Darwin. IOD compares two parts of the Indian Ocean. Neither a La Niña year nor a positive IOD guarantees rain at every Indian station.
🔒 ENSO is Pacific: El Niño often weakens India’s monsoon; La Niña often favours it. Neither result is guaranteed.
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