El Niño and La Niña are a natural part of the global climate system. They happen when the Pacific Ocean and the atmosphere above it changes from their neutral (normal) state for various reasons. Changes in the ocean surface temperatures affect tropical rainfall patterns and atmospheric winds over the Pacific Ocean, which impact the ocean temperatures and currents. El Niño and La Niña are opposite phases of what is called as the El Niño Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West). El Niño and La Niña occur every 3-5 years.
El Niño term is derived from the Spanish word which means “little boy”. During El Niño, the temperature is warmer than the usual sea-surface temperatures. It is a warming of the Pacific Ocean between South America and the International Date Line, centred directly on the Equator, and moves towards several degrees of latitude to the either side of the equator. It is laden with high air surface pressure in the Western Pacific. El Niño has a huge impact on season patterns because it makes the weather warmer and drier than the average temperature in the Northwest of Pacific and these regions experience decreased snowfall. El Niño also also reduces the strength of the Coriolis force. The wind speed of cyclones is low. Due to El Niño warm water approaches the coasts of South America which leads to decreased upwelling of nutrient rich deep water impacting fish populations.El Niño leads to heavy rains in Ecuador and Peru, heavy rains in Southern Brazil but drought in North East Brazil, drought in Zimbabwe, Mozambique,South Africa, warm winters in the northern half of the United States and Southern Canada. There is also drought and scant rainfall in Asia including India, Indonesia, and Philippines. Coral bleaching happens throughout the world due to El Niño and drought occurs in eastern Australia. El Niño thus influences weather patterns, ocean conditions and marine fisheries across large portions of the globe for an extended period of time.
La Niña is vastly different from El Niño. La Niña means “little girl” in Spanish. La Niña is also sometimes called as El Viejo, anti El Niño, or simply “a cold event”. La Niña leads to cooler than usual sea-surface temperatures. La Niña originates when cooler than normal ocean temperatures occur on the equator between South America and the International Date Line. La Niña has low air surface pressure in the eastern Pacific. When the trade winds blow unusually hard, La Niña happens. Due to La Niña, winters are wetter and it causes above average precipitation across the Northwest of Pacific and drier below average precipitation in the South West of Pacific. During a La Niña year, there is an increase in the strength of the Coriolis force. Cold water causes increased upwelling of deep cold ocean waters. La Niña has a greater tendency to trigger intense tropical cyclones as wind direction changes piling up water between Indonesia and nearby areas as winds from Africa onwards get blocked. La Niña causes extreme drought in Ecuador and Peru. It creates low temperatures and a very high pressure in Eastern Pacific. Heavy flooding happens in Australia. La Niña leads to high temperatures in Western Pacific, Indian Ocean, and off the coast in Somalia. La Niña causes good rains in India. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest part of the world.
El Niño and La Niña thus affect the world weather in opposite ways.
Written by- Urvi Pareek