El Nino

Why in news?

• A new study carried out by researchers of the Indian Institute of Science’s (IISc) Centre for Atmospheric and Oceanic Sciences (CAOS) has found that El Niño alone is not be blamed for droughts that in the Indian subcontinent.
• The study has found that nearly half of the droughts that occurred during the Indian summer monsoon season in the past century may have been driven by atmospheric disturbances from the North Atlantic region.

What is El Nino?

• El Niño is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific near the Peruvian coast.

Mechanism of El Nino:

What happens during normal years?

• A surface low pressure develops in the region of northern Australia and Indonesia and a high-pressure system over the coast of Peru.
• As a result, the trade winds over the Pacific Ocean move strongly from east to west.
• These carry warm surface waters westward, bringing convective storms (thunderstorms) to Indonesia, coastal Australia, and India.

What happens during El Nino years?

• Air pressure drops over large areas of the central Pacific and along the coast of South America and the pressure high in the Western Pacific is weakened.
• This results in the trade winds to be reduced and accumulation of Warm Ocean water along the coastlines of Peru and Ecuador.

Effects of El Nino:

• Severe droughts occur in Australia, Indonesia, India and southern Africa.
• El Nino and Indian monsoon are generally inversely related.
  • It adversely affects monsoon rainfall and cyclogenesis in Bay of Bengal. It even causes droughts in parts of the country.
• Warmer waters have a devastating effect on marine life existing off the coast of Peru and Ecuador - resulting in a decline of fisheries.

What is the Walker cycle?

• Walker cell is the longitudinal circulation across the equatorial Pacific driven by temperature and pressure gradients.
• In the walker cell, trade winds flow from areas of high pressure over the cooler eastern Pacific waters to areas of low-pressure form over the warmer eastern Pacific.
• During the El Nino, the Walker cell gets weakened or even get reversed.

Prelims Question

Consider the following statements regarding El Nino:
1.It causes warmer than average sea surface temperatures in eastern Pacific Ocean.
2.It generally has a positive impact on Indian monsoon circulations.
Which of the statements given above is/are correct? 
(a)1 only 
(b)2 only 
(c)Both 1 and 2 
(d)Neither 1 nor 2 

Answer to prelims question