From UPSC perspective, the following things are important :
Prelims level : Indian Monsson : Onset and Withdrawal
Mains level : El Nino and La Nina
Rainfall over the Southern peninsular region has been deficient so far due to prevailing La Nina conditions according to the India Meteorological Department (IMD).
Try this PYQ:
Q.La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino?
- La Nina is characterized by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.
- El Nino has an 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?
(a) Only 1
(b) Only 2
(c) Both 1 and 2
(d) Neither 1 nor 2
What is the Northeast monsoon?
- India receives rainfall during two seasons.
- About 75 per cent of the country’s annual rainfall is received from the Southwest monsoon between June and September.
- The Northeast monsoon, on the other hand, occurs from October to December and is a comparatively small-scale monsoon, which is confined to the Southern peninsula.
- After the complete withdrawal of the Southwest monsoon from the country takes place by mid-October, the wind pattern rapidly changes from the south-westerly to the north-easterly direction.
- Also called the winter monsoon, the rainfall associated with the Northeast monsoon is important for almost entire South India.
Why it is important?
- Tamil Nadu records about 48 per cent (447.4 mm) of its annual rainfall (943.7 mm) during these months, making it the key factor for undertaking agricultural activities and reservoir management in the state.
- Some South Asian countries such as Maldives, Sri Lanka and Myanmar also record rainfall from October to December.
Why there are distortions?
- The majority of districts in Tamil Nadu remain highly rain-deficient up this time.
- The period after the Southwest monsoon season, from October to December, is the peak time for cyclonic activity in the North Indian Ocean region — covering the Arabian Sea and the Bay of Bengal.
- The winds associated with the formation of low-pressure systems, depressions, or cyclones influence this monsoon, and therefore, the rainfall.
- Officials at IMD have linked it to the prevailing La Niña conditions in the Pacific Ocean.
La Nina link with the NE monsoon
- While La Niña conditions enhance the rainfall associated with the Southwest monsoon, it has a negative impact on rainfall associated with the Northeast monsoon.
- During La Niña years, the synoptic systems — low pressure or cyclones — formed in the Bay of Bengal remain significantly to the north of their normal position.
- Besides, instead of moving westwards, these systems recurve. As they lie to the north of their normal position, not much rainfall occurs over southern regions like Tamil Nadu.
Back2Basics: El Nino and La Nina
- While El Niño (Spanish for ‘little boy’), the more common expression, is the abnormal surface warming observed along the eastern and central regions of the Pacific Ocean (the region between Peru and Papua New Guinea).
- The La Niña (Spanish for ‘little girl’) is an abnormal cooling of these surface waters.
- Together, the El Niño and La Niña phenomena are termed as El Niño Southern Oscillation (ENSO).
- These are large-scale ocean phenomena which influence the global weather — winds, temperature and rainfall. They have the ability to trigger extreme weather events like droughts, floods, hot and cold conditions, globally.
- Each cycle can last anywhere between 9 to 12 months, at times extendable to 18 months — and re-occur after every three to five years.
- Meteorologists record the sea surface temperatures for four different regions, known as Niño regions, along this equatorial belt.
- Depending on the temperatures, they forecast either as an El Niño, an ENSO neutral phase, or a La Niña.