El Nino Southern Oscillation Current Affairs - 2020

IMD: El Nino to be neutral; Normal Monsoon rains for India

On March 19, 2020, the Indian Meteorological Department announced that the El Nino Weather Phenomenon is to remain neutral this year between May and July. This will bring in normal rains to India during South West Monsoon.

The Indian Monsoon is greatly affected by the El Nino and La Nina Weather Phenomenon. The neutral event of the weather phenomenon is addressed as ENSO Oscillation.

ENSO Neutral: The Usual Weather System in the Pacific

The trade winds that flows from the east to west (from South America to Australia) pushes warm water from the off coast of South America towards Eastern Australia and Asia. The waters are warmed up as they are in the tropical zone of the earth receiving direct sun rays. The warm water rises the air and gives plentiful rainfall in the region of Australia and Asia.

Also, the piling up of warm water in the western Pacific in turn pushes the cold under ocean waters towards eastern side of the Pacific (towards South America). This is called upwelling. This makes the climate in the western coast of South America cool.

Monsoon and ENSO

The ENSO phenomenon strengthens the trade winds that give good rains to India during Monsoon. It is the trade winds that get deflected due to Corolis force and blow as south west monsoon.

The heating up of Himalayas during summer creates a low pressure in the region. This low pressure attracts the moist high-pressure winds in the equator. They are moist due to the ENSO phenomenon.

Therefore, India receives good rainfall when ENSO is neutral

What is El Nino?

During El Nino, the ocean waters in the western Pacific (near Australia) warms up. This breaks the warm waters from reaching the Australian coast. This is because, the oceanic temperature in the middle of the Pacific is greater than its coastal. Hence, water starts moving from Australian coast and South American Coast towards the centre of the ocean. Rainfall now occurs in this part of the ocean, making both the coasts dry. Hence, the trade winds reaching near Indian waters are dry as well. This weakens Indian Monsoon.

Conditions normal for 2018 monsoon season: Weather scientists

Weather scientists have predicted normal monsoon in June-September 2018 monsoon season as prevailing conditions as well as neutral ENSO were favourable for good monsoon rainfall. India receives 89 cm of rainfall during four-month monsoon season, which is almost 75% of its annual rainfall. In 2017 monsoon season, country as whole had received rainfall that was 95% of its long-period average.

Key Facts

The most important favourable condition for good monsoon is near-neutral to neutral ENSO (El Nino Southern Oscillation) in equatorial Pacific Ocean, off coast of South America. Global climate models are showing near-neutral conditions prevailing in Pacific Ocean and it will remain this way through most of the year.

Moreover, La Niña conditions are present and equatorial sea surface temperatures (SSTs) are below average across central and eastern Pacific Ocean. The transition from La Niña to ENSO-neutral is most likely during March-May season, with neutral conditions likely to continue into second half of year. SST anomalies in eastern tropical pacific are ENSO-neutral during coming summer and hence normal monsoon is expected this year.

ENSO (El Nino Southern Oscillation)

ENSO refers to anomalies in SSTs in Pacific Ocean off coast of South America which has sometimes been observed to have near-decisive impact on monsoon rainfall. In El Nino, a warmer than usual SST is observed in Pacific Ocean off coast of South America . This condition is associated with suppressed monsoon rainfall in India. La Nina is opposite ENSO and is more favourable for monsoon. It is known to help monsoon rainfall in India. When anomalies (deviations from usual SST in the Pacific Ocean) are too small or absent, monsoon rainfall over India is normal.