Previous Year Question
La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino?
La Nina is characterised by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterised by unusually warm ocean temperature in the equatorial Pacific Ocean.
El Nino has adverse effect on South-West monsoon of India, but La Nina has no effect on monsoon climate.
Which of the statements given above is/are correct?
Correct Answer: D
Detailed Solution
Statement 1 is incorrect: La Niña is not an equatorial Indian Ocean phenomenon. It develops in the central and eastern equatorial Pacific Ocean.
El Niño: Surface waters in the central and eastern equatorial Pacific become warmer than normal.
La Niña: Surface waters in the same region become cooler than normal.
They constitute the warm and cold phases, respectively, of the El Niño–Southern Oscillation or ENSO.
Statement 2 is incorrect: La Niña does affect the monsoon climate. Generally:
During El Niño, Pacific trade winds weaken and the Walker circulation is altered. It is often associated with a weaker Indian south-west monsoon.
During La Niña, Pacific trade winds and the Walker circulation generally strengthen. This often favours normal or above-normal Indian monsoon rainfall.
The relationship is probabilistic, not certain. The Indian Ocean Dipole, snow cover and other oceanic-atmospheric conditions also affect the Indian monsoon. Therefore, every El Niño does not necessarily produce drought, and every La Niña does not necessarily produce excess rainfall.
During La Niña, warmer water and stronger convection are concentrated towards Australia and the western Pacific, potentially increasing rainfall and the risk of floods in that region.