El Niño Southern Oscillation (ENSO)
The connection between Earth’s oceans and atmosphere has a direct impact on the weather and climate conditions we experience. El Niño and La Niña, together called the El Niño Southern Oscillation (ENSO), are periodic departures from expected sea surface temperatures (SSTs) in the equatorial Pacific Ocean. These warmer or cooler than normal ocean temperatures can affect weather patterns around the world by influencing high and low pressure systems, winds, and precipitation. ENSO may bring much needed moisture to a region while causing extremes of too much or too little water in others.
Understanding the processes driving these types of interactions is a key component in improving forecasts and warnings. The NOAA Physical Sciences Laboratory studies multiple aspects of ENSO including its precursors, prediction, diversity, and climate and ecosystem impacts. This information can help keep communities safe and guide decisions related to issues such as water management, emergency planning, and ecosystem resilience.
More detailed information about ENSO can be found on the ENSO-101 tab.
What are El Niño and La Niña?
El Niño is characterized by unusually warm ocean temperatures along the the Equatorial Pacific, whereas La Niña is characterized by unusually cold ocean temperatures in this region. These variations from "normal" temperatures influence the tropical Pacific ocean—atmosphere system, which in turn impacts weather and climate around the globe. The term El Niño Southern Oscillation (ENSO) basically refers to both the El Niño and La Niña phenomena together. See this page for a more detailed explanation of what happens in the ocean and atmosphere during ENSO.
How often does ENSO occur?
While their frequency can be quite irregular, El Niño and La Niña events occur on average every 2—7 years. Typically, El Niño occurs more frequently than La Niña.
How long does ENSO last?
How will ENSO impact a particular region?
There has been a lot research investigating the effects of El Niño and La Niña on climate (temperature, rainfall, snowpack, climate extremes, etc.) around the world. However, these impacts can be different from year-to-year due to the varying nature of ENSO, and variations in the atmosphere–ocean system. The images below show typical El Niño and La Niña wintertime patterns for the U.S. Detailed information about worldwide impacts can be found on NOAA's El Niño Theme Page.
What is the Southern Oscillation Index (SOI)?
The cyclic warming and cooling of the eastern and central Pacific can be seen in the sea level pressure in the region. For example, when the pressure measured at Darwin, Australia is compared with that measured at Tahiti, the differences between the two can be used to generate an "index" number. A positive number indicates La Niña, and a negative number indicates El Niño. Historical and recent values can be found at NOAA's Climate Prediction Center .
- 2016 El Niño Rapid Response Field Campaign
An unprecedented field campaign to study El Niño while the event is ongoing.
- Climate Division Risk Maps
Does El Niño increase the chances of extreme temperatures or precipitation over the U.S.? PSL researchers have produced risk maps to investigate these questions.
- MEI ENSO Monitorings
Current and historic values of the Multivariate ENSO Index developed at PSL.
- California Drought
What can drought-stricken California expect from the El Niño winter forecast? PSL researchers contribute to the Drought Task Force report and FAQ.
- Hydrology in a Warming Climate; Hydrology That Might Have Been
Ongoing research into the effects of warming on snowpack and streamflow.
- Wind River/Greater Yellowstone Area and El Niño
PSL scientists collaborate with the North Central Climate Science Center to address ENSO risks of drought on the Wind River reservation.
News and Feature Stories
- Unprecedented effort launched to discover how El Niño affects weather
- Study confirms link between El Niño intensity and precipitation in California
- Andy Hoell contributes to Famine Early Warning Systems Network (FEWS NET) Alert on El Niño
- Researchers examine whether distinct 'flavors' of El Niño/La Niña may exist
- Taking the 'Noise' Out of Ocean Temperature Trends
- El Niño and Probability
- Global Patterns of the Risk of Seasonal Extremes Related to ENSO
- PSL ENSO Publications (1987–Present)
Here's a quick look at what's going on right now...
Sea Surface Temperature (SST)
More SST Maps: Weekly, Monthly, and Seasonal Averages
Outgoing Longwave Radiation (OLR)
More OLR Maps: Weekly, Monthly, and Seasonal Averages
Multivariate ENSO Index (MEI)
An experimental ENSO monitoring tool showing departures from normal conditions in the tropical Pacific from 1950-present.
Current ENSO Related Indices
See how the current atmosphere/ocean state compares with others for a collection of ENSO indices. Time-series plots and latest values of the indices are also available.
The ability to forecast El Niño and La Niña events is extremely important as these events tend to be associated with consistent climate variations in the tropics and can even influence the atmosphere around the world. There are two types of forecasts: those obtained from various ocean–atmosphere models and those obtained from statistical models. These models vary in their skill and sometimes can even do better during certain phases of ENSO than others. Forecasters try to take all this in account when making predictions.
PSL Experimental ENSO Forecasts
Linear Inverse Modeling SST/ENSO Forecast
Experimental statistical forecasts of SST anomalies based on current initial conditions. SST data used in these forecasts have been provided by NCEP, courtesy of R. W. Reynolds. Contour interval is 0.3 degrees C.
- Collection of Other ENSO Forecasts (NOAA El Niño Theme Page)
What years are ENSO years?
Because ENSO events differ in their strength, coverage, and seasonality, there isn't unanimous agreement on what constitutes and ENSO event. But, there are broad agreements and you can find some of the lists researchers have used along with how they chose those years. The list in the right column represents ENSO years based on PSL's Extended Multivariate ENSO Index (MEI.ext).
You may also be interested in:
Animations of Selected Past Events
1982–1983 El Niño
2010–2011 La Niña
1991–1992 El Niño
1988–1989 La Niña
1997–1998 El Niño
1999–2000 La Niña
Past ENSO Years
Comparison of Timeseries of Historic Events
Temporal evolution of El Niño and La Niña events indicated by the MEI.v2. Shown are the top 5 warm and cold non-overlapping events since 1979. Year 0 corresponds to the year of the event in the legends. Click on image to enlarge.
Explore Our Analysis Tools
El Niño and La Niña can cause the "seasonal climate" – the cumulative effects of the weather over a season – to deviate from normal at many places around the globe. The following PSL pages can be used to analyze what happened during past El Niños and La Niñas and provide a guide to what may happen in the future.
This tool allows single or comparison plots of seasonal averaged variables in relation to El Niño and La Niña over the US and the globe.
See what the seasonal cycle of different variables during an average El Niño and La Niña look like.
Plot average signals based on historical data of global surface temperature and precipitation.
Composite Wintertime US Temperature and Precipitation Anomalies and Standardized Anomalies
Given an El Niño or La Niña condition, what are the odds of getting a warm versus a cold season? A wet versus a dry season?
How Events Differ
These plots give an indication of how similar and how different the atmosphere can be during events.
Datasets Useful for Research
Sea Surface Temperature (SST)
Gridded SST datasets are available for monthly means and for daily. Values can be mean or anomalies. Gaps usually exist in SST dataets both in space and time. Different datasets use different models to fill in gaps.
|Datasets||Areal Coverage||Grid Size||Time Step||Time Coverage||Levels|
|CRU Air Temperature and Combined Air Temperature/Marine Anomalies V4||Global||5.0°x5.0°||Monthly||1850-2013||None|
|NCEP GODAS ocean analysis||Global||.3°x.3°||Monthly||1980-present||40|
|NCEP/NCAR Reanalysis||Global||2.5°x2.5°, T42 Gaussian, T62 spectral||4X Daily, Daily, Monthly||1948-present||17 pressure levels, 28 spectral|
|NOAA Extended Reconstructed SST V4||Global||1.0°x1.0°||Monthly||1854-present||None|
|NOAA High-resolution Blended Analysis of Daily SST and Ice.||Global||.25°x.25°||Daily||1981-present||None|
|NOAA Global Surface Temperature (NOAAGlobalTemp)||Global||5.0°x5.0°||Daily||1880-present||None|
|NOAA Optimum Interpolation (OI) SST V2||Global||1.0°x1.0°||Monthly,Weekly||1981-present||None|
|COBE-SST2 Sea Surface Temperature||Global||1.0°x1.0°||Monthly||1850-2012||None|
|NODC (Levitus) World Ocean Atlas 1994||Global||1.0°x1.0°||Monthly,Annual||Climo||None|
|NODC (Levitus) World Ocean Atlas 1998||Global||1.0°x1.0°||Monthly,Annual||Climo||None|
Outgoing Long Wave Radiation (OLR)
OLR is a measure of tropical convection and has been available via satellite observations since the early 1970's. We make available gridded interpolated values as well as the provided directly from NCEP (which are more recent).
|Datasets||Areal Coverage||Grid Size||Time Step||Time Coverage||Levels|
|Interpolated OLR||Global||2.5°x2.5°||Daily,Monthly||1979-near present||None|
While ENSO is a process that varies both in space and time, it can be convenient to use single time series to represent in monitoring and analysis. Some of these time series are SST averages in a specific region of the tropical Pacific while others use more than 1 variable to attempt to capture more of the dynamical processes that occur in ENSO.
|Oceanic Niño Index (ONI)||SST 5N-5S, 170W-120W||1950-present|
|Niño 1.2||SST 0-10S, 90W-80W||1870-present|
|Niño 3||SST 5N-5S, 150W-90W||1870-present|
|Niño 3.4||SST 5N-5S, 170W-120W||1870-present|
|Niño 4||SST 5N-5S, 160E-150W||1870-present|
|Multivariate ENSO index: MEI||Tropical Pacific||1979-present|
|Extended Multivariate ENSO index: MEI.ext||Tropical Pacific||1871-2005|
|Trans-Niño Index (TNI)||Difference Niño 1.2 and Niña 4||1870-present|
|Southern Oscillation Index (SOI)||Difference of Surface Pressure of Tahiti and Darwin||1870-present|
As ENSO impacts weather and climate in general, researchers need to potentially look at all atmospheric and ocean variables. PSL maintains an extensive collection of gridded datasets including our 20th Century Reanalysis(1851-2014). Other dataset can be found from links on PSL's data information webpage. Some other NOAA sites also link to ENSO related datasets: for example, NOAA/CPC has an ENSO data/info list.
Resources and Additional Information
NOAA Boulder Public Affairs Officer:
Theo.Stein@noaa.gov, (303) 497-6288