RAS question
La Niña is characterized by:
Correct answer: (A) Unusual cooling of eastern Pacific Ocean waters.
La Nina is characterised by unusually cool ocean surface temperatures in the central and eastern Pacific, making it the cold phase of ENSO.
Explanation
La Nina is the cold counterpart of El Nino within the El Nino-Southern Oscillation, a climate pattern linked to fluctuating ocean temperatures in the central and eastern equatorial Pacific and changes in the atmosphere above it. The WMO explains that El Nino is marked by unusually warm ocean surface temperatures in this region, while a La Nina event is marked by unusually cool temperatures in the same region, along with stronger prevailing east-to-west surface winds. That is why the option referring to unusual cooling of eastern Pacific Ocean waters captures the defining feature. La Nina generally strengthens the Indian monsoon, often bringing above-normal rainfall, and is also associated with higher Atlantic hurricane activity.
Why the other options are wrong
- (B) La Nina is not a no-effect condition; it is linked to a stronger Indian monsoon and higher Atlantic hurricane activity, while WMO treats it as an ENSO phase with ocean-atmosphere changes.
- (C) Warming of the Arctic does not define La Nina; the World Meteorological Organization places La Nina in the central and eastern equatorial Pacific, not in the Arctic.
- (D) Warming of the Pacific describes the warm El Nino side of ENSO, whereas La Nina is identified by unusually cool Pacific surface temperatures in the relevant region.
Concept
This tests ENSO basics under climatology, especially the contrast between El Nino and La Nina and their monsoon links. It recurs in RAS because Pacific sea-surface temperature anomalies are a standard explanation for Indian monsoon variability.