El Nino and La Nina
By influencing global temperatures and precipitation, the El Niño/Southern Oscillation (ENSO) significantly impacts Earth’s ecosystems and human societies. El Niño and La Niña are opposite extremes of the ENSO, which refers to cyclical environmental conditions that occur across the Equatorial Pacific Ocean. These changes are due to natural interactions between the ocean and atmosphere. Sea surface temperature, rainfall, air pressure, atmospheric and ocean circulation all influence each other. A satellite image of the Earth showing an abnormally warm area near the equator off the West Coast of South America. Satellite sea surface temperature departure in the Pacific Ocean for the month of October 2015, where darker orange-red colors are above normal temperatures and are indicative of El Niño. (Image credit: NOAA)
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What is El Niño? What is La Niña?
An El Niño condition occurs when surface water in the equatorial Pacific becomes warmer than average and east winds blow weaker than normal. The opposite condition is called La Niña. During this phase of ENSO, the water is cooler than normal and the east winds are stronger. El Niños typically occur every 3 to 5 years.
ENSO-Neutral or average conditions across the tropical Pacific Ocean. Climate.gov schematic by Emily Eng and inspired by NOAA PMEL. The rise of El Niño and La Niña How do El Niño and La Niña events form and increase in strength? The key is in the ocean-atmosphere coupling across the tropical Pacific Ocean.
How ENSO impacts humans?
El Niño, La Niña, and the neutral condition all produce important consequences for people and ecosystems across the globe. The interactions between the ocean and atmosphere alters weather around the world and can result in severe storms or mild weather, drought or flooding. Beyond “just” influencing the weather, these changes can produce secondary results that influence food supplies and prices, forest fires, and create additional economic and political consequences. Famines and political strife can result from these environmental conditions.
(top) The sea surface temperature (shaded contours), 10-meter wind (vectors), and (bottom) rainfall departures from average in June – August during an average Atlantic Niño. The gray dots in the bottom panel indicate that the rainfall departures are statistically significant (5% significance level), indicating a high degree of confidence that the rainfall departures are associated with Atlantic Niño. Climate.gov figure adapted from Vallès‐Casanova et al. (2020). Do you know that El Niño has a little brother? His name is Atlantic Niño, and he has an uncanny resemblance to his big brother: Like El Niño, Atlantic Niño is characterized by warmer-than-average sea surface temperatures in the eastern equatorial basin and weaker-than-average trade winds throughout the east-central equatorial Atlantic. What are some of ENSO’s impacts? Ecosystems and human communities can be positively or negatively affected. For example, in the Southern United States, during the fall through spring, El Niño usually causes increased rainfall and sometimes destructive flooding. La Niña, however, usually causes drier weather in the South, but the Northwest tends to be colder and wetter than average. Even though El Niño occurs in the Pacific Ocean, it often reduces the number of hurricanes that form in the Atlantic Ocean. Conversely, La Niña events tend to be related to an increase in the number of Atlantic hurricanes.
Food production is impacted by ENSO. Changes in ocean temperatures and currents that happen during El Niño impact marine life. This can impact individuals who make a living fishing and consumers who depend on certain fish for food. Agriculture is of course very dependent on climate and weather, as a result ENSO’s influence on rainfall and temperature have important consequences for food production and availability.
Redoubt Volcano viewed from the northwest following the April 4, 2009 eruption. Credit: R. G. McGimsey, USGS.
Can volcanic eruptions cause El Niño? Maybe, maybe not
Volcanic eruptions have had HUGE impacts on the global climate by cooling Earth. It’s only natural to wonder, if the planet is affected by volcanic eruptions, can ENSO be? The origin of the name The origin of the name “El Niño” dates to the 1800’s, when fishermen on the Pacific coast of South America would notice that a warm ocean current would appear every few years. Fish catches would drop drastically, negatively affecting the food supply and livelihood of the communities of coastal Peru. This warm water would arrive around Christmastime. Referring to the birth of Christ, they named the warm ocean waters, El Niño, which means “the boy” in Spanish. Fishing in this region is best during La Niña years when cold upwelling ocean water brings rich nutrientsoffsite link from the deep ocean, resulting in an increase in the number of fish caught.
The Southern Oscillation is a coherent interannual fluctuation of atmospheric pressure over the tropical Indo-Pacific region
- It is the atmospheric component of a single large-scale coupled interaction called the El Niño-Southern Oscillation (ENSO)
- The Southern Oscillation describes changes in air pressure patterns in the Southern Pacific Ocean between Tahiti, in the middle of the southern Pacific Ocean, and Darwin, Australia, to the west 2. Normally, lower pressure over Darwin and higher pressure over Tahiti encourages air movement from east to west 2. The Southern Oscillation Index (SOI) tracks the atmospheric part of the ENSO pattern 3.