RAS question
Which of the following correctly describes the El Nino phenomenon?
Correct answer: (D) Warming of Pacific Ocean waters near Peru/Ecuador coast.
El Nino is the warm phase of ENSO, marked by unusual warming of central and eastern equatorial Pacific waters, including the sea surface off Peru and Ecuador.
Explanation
El Nino is not a general warming of any ocean; it is the warm oceanic phase of the El Nino Southern Oscillation. The WHO describes ENSO as a naturally occurring climate phenomenon involving fluctuating ocean temperatures in the central and eastern equatorial Pacific, linked with atmospheric changes. During an El Nino event, sea-surface warming occurs and the normal nutrient-rich cold-water upwelling off the Peru-Ecuador coast is suppressed. That is why the option locating the warming near Peru and Ecuador in the Pacific is the precise description. For Indian geography, the exam relevance comes from the existing link with a weaker Indian monsoon and drought risk, while La Nina is the cooler counterpart that tends to strengthen the monsoon.
Why the other options are wrong
- (A) Cooling of Pacific waters describes La Nina, the cool ENSO phase, not El Nino.
- (B) El Nino is tied to warming in the central and eastern equatorial Pacific, not to warming of the Indian Ocean.
- (C) The Atlantic Ocean is outside the ENSO setting described in the question and the source, which place the phenomenon in the equatorial Pacific.
Concept
This tests the climatology link between ENSO and the Indian monsoon, a recurring RAS theme because drought, rainfall variability and monsoon behaviour often turn on ocean-atmosphere interactions. The key is to separate El Nino, La Nina and the Indian Ocean Dipole without mixing their ocean basins.