El Nino and La Nina
Why in news :
- India is experiencing a colder than normal winter thanks to the north-south winter flow set up by the climate phenomenon known as La Nina.
- The La Niña itself is going on for a record-breaking third consecutive year.
- Now, forecasts for the 2023 fall and winter are predicting that there is a 50% possibility for its companion phenomenon, the El Nino to occur.
What are El Niño and La Niña?
- El Nino refers to a band of warm water spreading from west to east in the equatorial Pacific Ocean.
- El Nino is an abnormal warming of the surface waters in the eastern tropical Pacific Ocean in comparison to the western Pacific.
- This occurs every four to 12 years. As temperatures rise, rainfall patterns change around the world. Some places receive more rain, some get less.
- The years in which an El Nino occur are called ‘El Niño years’, and global weather patterns in that year tend to be anomalous in certain ways.
- La Niña occurs when the band of water spreads east-west and is cooler.
- Both phenomena can have drastic effects on economies that depend on rainfall.
- An El Niño year creates a miniature global-warming crisis, since the warm water spreading across the tropical Pacific releases a large amount of heat into the atmosphere.
- Monsoon in India is often weaker during El Nino. But this is not always so.
- It is estimated that 60% of all droughts in India in the last 130 years have coincided with an El Nino.
- These have been years when rainfall was over 10% less than normal.
- However, not every El Nino has caused a drought or bad monsoon.
- The effect of Lanina are that it creates heavy monsoons throughout India and Southeast Asia.
- It creates a drought-like situation in Peru and Ecuador.
- It causes wet and cool winters in south-eastern Africa and wet weather conditions in eastern Australia.
Cyclone formation and monsoons :
- A transition from a La Niña winter to an El Niño summer historically tends to produce a large monsoon deficit, on the order of 15%.
- This means pre-monsoon and monsoon circulations tend to be weaker in an El Niño year.
- The vertical shear (change in the intensity of winds from the surface to the upper atmosphere) tends to be weaker as well.
- This in turn can favour enhanced cyclone formation.
- Intraseasonal or subseasonal timescale variability in sea-surface temperature and winds is also very important for cyclogenesis over the northern Indian Ocean.
- These timescales denote the durations for which certain temperature and wind characteristics persist in the pre and post-monsoon periods.
- The net effect is for cyclogenesis to be subdued in an El Niño year.
Syllabus : Prelims + Mains; GS1- Geography