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What is the El Niño Southern Oscillation? 

The El Niño-Southern Oscillation (ENSO) is a cyclical shift in wind patterns and ocean circulation across the tropical Pacific Ocean with global effects on weather and climate. 

In normal conditions, easterlies – winds that blow in tropical latitudes from the Pacific coast of the Americas towards Asia – drive a continuous buildup of warm water off the coasts of Asia and upwelling of cool water in the Eastern Pacific. During an El Niño period, these winds weaken and change direction, pushing this warm water back towards the Americas and driving upwelling of colder waters off of Asia. La Niña is a near reversal of this pattern, when the easterlies become stronger than usual, with cooler waters in the Eastern Pacific and even warmer water in the Western Pacific. 

The mechanism that causes these changes in wind patterns, and that eventually restores the usual easterlies, is unclear. What is clear is that effects of this cycle are varied and complex and have major impacts on global weather, affecting ocean circulation, storm formation, and precipitation patterns. During El Niño, droughts become more common in southeast Asia, while heavy rainfall can occur in South America and the west coast of the United States. Upwelling areas off the North and South American coasts change, which can reduce the nutrients available near the ocean’s surface and lead to lower catches for local fisheries. Conversely, La Niña can drive severe rainfall and flooding in the United States Pacific Northwest and Canada, and cause more severe hurricanes in the Atlantic. 

How Do Scientists Monitor El Niño? 

Missions like Surface Water and Ocean Topography (SWOT), Sentinel 6 Michael Freilich, and Sentinel 6B can monitor variations in sea surface height across the world’s ocean basins. The height of the surface is a reflection of the amount of heat stored in the water, as warm water expands to fill more space than cooler water. These satellite missions can track the buildup of warm water in the Western Pacific, and the sloshing movement of warm water masses as they move eastwards that signals the start of an ENSO period.

The satellites of the Gravity Recovery and Climate Experiment (GRACE and GRACE-FO) track changes in water mass and storage around the planet, showing scientists where excess or depleted rainfall is changing the amount of freshwater on land at different phases of ENSO.

The Global Precipitation Mission (GPM) and Tropical Rainfall Monitoring Mission (TRMM) capture how ENSO affects global and regional precipitation. Missions like the Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite and the Visible Infrared Imaging Radiometer Suite (VIIRS) instruments can track changes in ocean conditions that can affect phytoplankton populations and global fisheries. 

 

What Do Scientists Do with El Niño Observations? 

These observations can help communities understand and prepare for the weather changes caused by the El Niño. Long-term observations of ENSO conditions are also used to further improve climate models. Tracking the ENSO cycle is also vital for climate resilience. El Niño can bring higher temperatures, unpredictable storm formation, and changes in rainfall patterns in some regions. 

Learn How to Use El Niño-Southern Oscillation (ENSO) Data

View All El Niño-Southern Oscillation (ENSO) Learning Resources
Access a range of webinars, tutorials, data recipes, and data stories to enhance your knowledge of Earth Observation data.
ARSET SWOT thumbnail image
Monitoring Global Terrestrial Surface Water Height using Remote Sensing
This ARSET training focuses on introducing SWOT freshwater data products and their applications for water resources and disaster management.
sea surface height grid at the spatial resolution of 2 degrees
Sea Surface Height Grids With Different Spatial Resolutions
SWOT and ECCO can measure sea surface height at different resolutions for monitoring the ocean's vertical heat, carbon transport, and other processes.
comparison of sea level anomalies between el nino events of 2007 and 2015
Sea Level Satellites Monitor How This Year’s El Niño Is Shaping Up
Sea surface height data from the Sentinel-6 Michael Freilich mission reveal complex interactions between the ocean and the atmosphere that affect global weather and climate such as El Niño.
El Nino conditions in the Pacific Ocean from 2023
Pacific Ocean Conditions Favorable for Winter 2023/2024 El Niño Development
Satellite data provides indicators of El Niño events.
Discover and Visualize El Niño Data
NASA data help us understand Earth's changing systems in more detail than ever before, and visualizations bring these data to life, making Earth science concepts accessible, beautiful, and impactful.
Data visualization is a powerful tool for analysis, trend and pattern recognition, and communication. Our resources help you find world-class data visualizations to complement and enhance your research. We also have tools and tutorials to help you translate El Niño data into compelling visuals.
El Niño Data Catalog
Image from May 26, 2026 of sea surface temperature anomalies indicating warmer than normal temperatures.
Sea surface temperature anomalies on May 26, 2026, from the Group for High Resolution Sea Surface Temperature (GHRSST) level 4 analysis.

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