What Is El Niño?


Credit: Pixabay 

El Niño occurs every 3-7 years in the Pacific Ocean. It is a weather pattern that generally occurs in sync with La Niña. During El Niño, winds cause warm surface water from the equator to move east towards Central and South America. El Niño can cause more rain in South and Central America as well as in the United States. The event affects weather in different aspects all over the world. La Niña also affects weather across the globe, only in the opposite way. 

El Niño is an unusual warming of surface waters in the tropical Pacific Ocean. La Niña is the unusual cooling of surface waters in the tropical Pacific Ocean. These events switch every 3-7 years and are in sync with each other. This weather pattern is referred to as ENSO, El Nino-Southern Oscillation (ENSO). The occurrence takes into effect several components, the largest effect being on ocean temperature. Ocean temperature also has a large effect on the wind temperature, which changes weather. Seasons are affected by these two components. During a warm year, summers get hotter and winters are warmer. During a colder year, summers are cooler and winters are colder. 

Ocean Temperature

Ocean temperatures greatly affect weather across the globe. In places where the ocean is generally warm there is more rain and clouds. These warmer places are closer to the equator and the sun heats the ocean up throughout the day. 

In years where El Niño is in effect, more rain clouds form out at sea and bring in rain from the warmer water. While this is occurring, other places in the world have drought, causing forest fires or lakes to dry up. These odd weather patterns are not uncommon during El Niño years. 

During El Niño, the thermocline (how deep the heat penetrates the water) can be extended and stretch as far as 500 ft below the surface. This amount of heat does not allow for cold water to bring nutrients from the depths to support normal sea life and can cause die offs and migrations of normally productive fish.


Trade Winds generally blow to the west across the Pacific which causes cooler waters to rise to the surface and warmer water to cool in the middle of the Ocean. The movement of deeper colder water to replace warmer water is known as upwelling. 

Upwelling brings nutrients and phosphates to the surface, as well as cooler water. Phytoplankton use these to grow through photosynthesis. Many animals including clams, fish, and whales eat phytoplankton. Phytoplankton are a key for many species that provide for the South American seafood industry including anchovy, sardine, mackerel, shrimp, tuna, and hake.

Credit: Pixabay 


During the fall and winter in some El Niño years winds are weaker than usual. The wind blows the other way in October which causes warm surface water to move north toward California and south toward Chile. 

As El Niño begins or ends, there are different weather effects that can occur. These include more tornadoes in the midwest, more hurricane activity in the Atlantic and Gulf of Mexico, and changes in the central, not eastern, Pacific. 

The National Oceanic and Atmospheric Administration (NOAA) operates a network of scientific buoys which measure air temperatures, currents, winds, and humidity. The buoys are located in around 70 locations around the southern Pacific Ocean. This monitoring helps scientists find new details and discoveries about climate and weather effects.