El Niño Southern Oscillation (ENSO)

ENSO 101

Some Basics

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.

A very strong El Niño in 2016 – large 'red tongue' in equatorial Pacific. (Credit: NOAA/NESDIS)

A very strong El Niño in 2016 – large 'red tongue' in equatorial Pacific. (Credit: NOAA/NESDIS)

A La Niña event – large blue area in equatorial Pacific. (Credit: NOAA/NESDIS)

La Niña event – large blue area in equatorial Pacific. (Credit: NOAA/NESDIS)

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.

Typical wintertime El Niño pattern. (Credit: climate.gov)

Typical wintertime El Niño pattern. (Credit: climate.gov)

Typical wintertime La Niña pattern. (Credit: climate.gov)

Typical wintertime La Niña pattern. (Credit: climate.gov)

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 .

Learn More

Our Research

Selected Topics

• 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 V2 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 contributed to the Drought Task Force report
• 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.

Current Conditions

Below is a quick look at what's going on right now. You may also want to check out the Climate.gov ENSO Blog .

Sea Surface Temperature (SST)

Outgoing Longwave Radiation (OLR)

Animations

Marine Heat Waves (PSL's Marine Heatwave Page)

Multivariate ENSO Index (MEI)

An experimental ENSO monitoring tool showing departures from normal conditions in the tropical Pacific from 1950-present.

More about the MEI

Forecasts

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.

Official NOAA ENSO Forecasts from the Climate Prediction Center

• ENSO Conditions, Outlooks, Diagnostics
• Seasonal SST Forecasts
• ENSO Diagnostic Discussion and Advisory Bulletin

PSL Experimental ENSO Forecasts

Linear Inverse Modeling SST/ENSO Forecast

Experimental forecasts (sample images below) of numerous tropical fields, including precipitation, outgoing longwave radiation (OLR), sea surface temperature (SST), and sea surface height (SSH); other variables may become available at a later date.

More Information

• Collection of Other ENSO Forecasts (NOAA El Niño Theme Page)

Past Events

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 Historic Climate Relationships

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.

Updated! Global/US Seasonal ENSO Related Variables

New! FEWS NET: Historic ENSO-Related Climate Impacts

Updated!Selected Variables by month for El Niño/La Niña including composite mean and inter-event standard deviation with many different types of variables.

Comparisons of Different El Niño and La Niña Events
Animations, plots, and more: These links give an indication of how similar and how different the atmosphere/ocean can be during events.

Seasonal Extremes

Effects on Seasonal Climate Extremes of Temperature and Precipitation Over the US
("Risk Plots")

Datasets Useful for ENSO 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.

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).

Precipitation

For ENSO, precipitation is both associated with changed forcing in the tropics and also is a response to changed flow over the globe.

Climate Indices relating to ENSO

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. Some indices measure the diffrences between events.

Other Datasets

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 NOAA-CIRES-DOE Twenthieth Century Reanalysis V3. 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

Related Websites

• NOAA Climate.gov ENSO Page
• NOAA Climate Prediction Center El Niño Page
• NOAA Pacific Marine Environmental Laboratory El Niño Theme Page
• Western Regional Climate Center ENSO Page

Definitions

• Glossary of Climate-Related Terms

Videos

• Understanding El Niño (NOAA climate.gov)
• Understanding La Niña (NOAA climate.gov)
• Observing El Niño (NOAA 'Ocean Today')
• Potential Impacts of El Niño in Colorado (by NOAA/PSL and CIRES)

Media Contact

• NOAA Boulder Public Affairs Officer:
  Theo.Stein@noaa.gov, (303) 497-6288