La Nina Current Affairs - 2020

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Facts Box: Effects of El-Nino, Equinod and IOD on Indian Monsoon, 2019

The ongoing frenetic of the North-East Monsoon in the Peninsular India were supported by the same factors that propelled the South-West monsoon. The Indian monsoon of 2019 saw a neutral Pacific (neither El Nino nor La Nina), a positive Indian Ocean Dipole (IOD) and a positive Equatorial Indian Ocean Oscillation (EQUINOO).

El nino

  •  The variation in sea surface temperature drives the Indian Ocean and the Pacific phenomena and thereby Indian Monsoon.
  • The El Nino is a phenomenon in the equatorial Pacific where the temperature rises over a threshold of 0.5 degree Celsius. During El Nino the Equatorial East Pacific warms up relative to the west and has adverse impact on Indian monsoon.
  • The monsoon winds and rains are strong during La Nina and weak during El Nino. La Nina years bring heavy rains and El Nino years are dry.
  • Between 1950 and 2012, there were 16 La Nina years with monsoon rains ending up above or around average every time. Also, there were 14 other occasions. The 2002 was the driest monsoons in all these years when El Nino occured.
  • The weak El Nino in the Pacific Ocean this year is one of the reasons for rainfall deficit in the month of June.

IOD

In a positive IOD, the western basin of the Indian Ocean warms up creating a low pressure. This rises warm air clouds to set up storms and heavy rains in the South and South east Asia. A positive IOD aids in Indian monsoon. 2019 Monsoon witnessed a positive IOD

EQUINOD

The positive EQUINOD translates more or less positive IOD. The Positive EQUINOD aids in North East Monsoon. 2019 monsoon witnessed a positive EQUINOD.

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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.

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