El Niño Southern Oscillation (ENSO)
- El Nino translates to ‘little boy’ or ‘Christ child’ in Spanish.
- El Nino is a climate pattern that denotes the unusual warming of surface waters in the eastern tropical Pacific Ocean along the coast of Peru and Ecuador.
- The El Nino event is not a regular cycle, and is not predictable and occur irregularly at intervals of two- to seven-years.
- El Niño usually lasts for a few weeks to a few months and normally begins around Christmas.
- Sometimes an extremely warm event can develop which can last for much longer time periods.
- Such a strong El Niño developed in 1991 and lasted until 1995, and another began from fall of 1997 to spring of 1998.
- It is more frequent than La Nina.
Impact of El Nino on Monsoon:
- El Nino and Indian monsoon are often inversely related.
- The cool surface water, off the Peruvian coast becomes warm due to El Nino.
- When the water is warm, the normal trade winds loose intensity or reverse their direction.
- Hence, the flow of moisture-laden winds becomes directed towards the coast of Peru from the western Pacific i.e., the region near northern Australia and South East Asia.
- This causes heavy rains in Peru during the El Nino years which robs the Indian subcontinent of its normal monsoon rains.
- The higher the temperature in the Peruvian coast, the larger the shortage of rainfall in India.
- La Nina translates to ‘little girl’ in Spanish which is also known as El Viejo or ‘cold event’.
- La Nina is the “cool phase” of ENSO and is a pattern which denotes an unusual cooling of the tropical eastern Pacific.
- La Nina events can last for one to three years, unlike El Nino, which usually lasts no more than a year.
Impact of La Nina:
- La Nina is caused due to a build-up of cooler-than-normal waters in the tropical Pacific which is the area of the Pacific Ocean between the Tropic of Cancer and the Tropic of Capricorn.
- La Nina events can cause higher than normal rain conditions over south-eastern Africa and northern Brazil.
- Moreover, strong La Nina events can cause catastrophic floods in northern Australia.
- Drier-than-normal conditions are observed along the west coast of tropical South America, the Gulf Coast of the United States, and the pampas region of southern South America during formation of La Nina.
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