RAS question
El Nino refers to:
Correct answer: (D) Abnormal warming of sea surface temperatures in the central and eastern tropical Pacific Ocean.
El Nino refers to the abnormal warming of sea surface temperatures in the central and eastern tropical Pacific Ocean.
Explanation
El Nino is identified by unusual warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean. The WMO describes it as a periodic, large-scale warming of ocean surface temperatures in that region, coupled with changes in tropical atmospheric circulation, including winds, pressure and rainfall patterns. That is why option D is precise: it locates the warming in the central and eastern tropical Pacific, not in the Indian Ocean. For the Indian monsoon, the key RAS link is that El Nino can weaken monsoon winds by altering Walker Circulation and reducing the pressure gradient that helps drive them.
Why the other options are wrong
- (A) Strengthening of trade winds points away from El Nino because El Nino weakens trade winds, while La Nina is associated with stronger trade winds.
- (B) Warming of the Indian Ocean is not the definition of El Nino; the WMO places El Nino in the central and eastern equatorial Pacific Ocean.
- (C) Abnormal cooling of Pacific sea surface temperatures describes La Nina, whereas El Nino is the abnormal warming of those waters.
Concept
This tests the climatology concept of ENSO and its link with Indian monsoon variability. It recurs in RAS because Pacific sea-surface temperature anomalies help explain recurring questions on rainfall, winds and drought risk.