El Niño Southern Oscillation (ENSO)

El Nino


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 ESRL Physical Sciences Division 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.

Drought photo credit: USGS
Flooding photo credit: FEMA
Coral bleaching photo credit: NOAA
ENSO impacts can include hazards to people and property from droughts, heatwaves, and floods. Ecosystems are also at risk, for example corals may become bleached by distress from unusually warm ocean temperatures.

Animation showing average sea surface temperature anomalies over the past year. Updated weekly. (Larger View)

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.

2016 El Nino (Credit: NOAA/NESDIS)
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)
La Nina, 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?

El Niño typically lasts 9–12 months, and La Niña typically lasts 1–3 years. Both tend to develop during March–June, reach peak intensity during December–April, and then weaken during May–July. However, prolonged El Niño episodes have lasted 2 years, and even as long as 3-4 years.

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 in 2016 – large 'red tongue' in equatorial Pacific. 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)
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

For Students and Teachers

Data In the Classroom (NOAA/NESDIS)
Investigating El Niño Online Activity

El Niño Student Activity (NOAA/OAR)
Student Booklet
Teacher Information on El Niño
Activity Key

Our Research

Selected Topics

  • 2016 El Niño Rapid Response Field Campaign
    An unprecedented field campaign to study El Niño while the event is ongoing.
  • 2015 El Niño Situational Awareness
    A collection of research about the 2015-2016 event that addresses potential risks and impacts.
  • Climate Division Risk Maps
    Does El Niño increase the chances of extreme temperatures or precipitation over the U.S.? PSD researchers have produced risk maps to investigate these questions.
  • MEI ENSO Monitorings
    Current and historic values of the Multivariate ENSO Index developed at PSD.
  • California Drought
    What can drought-stricken California expect from the El Niño winter forecast? PSD 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
    PSD scientists collaborate with the North Central Climate Science Center to address ENSO risks of drought on the Wind River reservation.

Current Conditions

Here's a quick look at what's going on right now...

Sea Surface Temperature (SST)

Today's SSTs

today's SST

Today's SST Anomalies

today's SST anomalies

Outgoing Longwave Radiation (OLR)

Today's OLR

today's OLR

Today's OLR Anomalies

today's OLR anomalies


2015 Average Weekly Sea Surface Temperature Anomalies

2015 Average Daily Sea Level Height Anomalies

Multivariate ENSO Index (MEI)

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

current MEI

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.

PSD 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.

Linear Inverse Modeling Seasonal Plot

Experimental Tropical C-LIM "Coupled" LIM Forecast

C-LIM is user to create forecasts of Tropical Convection, Wind, and SST for out to 200 days.

plot lag4

More Information

Past Events

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 PSD'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

El Niño




La Niña


Years are determined from Dec-Jan-Feb (DJF) values of the PSD MEI.ext index. ENSO events are most clearly defined in northern winter (DJF), both in terms of impacts and robustness with regard to the ENSO index used. Other seasons have impacts, too, but do not necessarily match the winter seasons.

Comparison of Timeseries of Historic Events

MEI of 7 strongest El Nino events since 1950 vs. 2009-10
MEI of 7 strongest La Nina events since 1949

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 PSD 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.

Average Climate

Seasonal Extremes

How Events Differ

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 dataaets 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 Global5.0°x5.0° Monthly1850-2013None
ICOADS Global2.0°x2.0°,1.0°x1.0° Monthly1800-presentNone
Kaplan SST Global5.0°x5.0° Monthly1856-presentNone
NCEP GODAS ocean analysis Global.3°x.3° Monthly1980-present 40
NCEP/NCAR Reanalysis Global2.5°x2.5°, T42 Gaussian, T62 spectral 4X Daily, Daily, Monthly1948-present17 pressure levels, 28 spectral
NOAA Extended Reconstructed SST V4 Global1.0°x1.0° Monthly1854-presentNone
NOAA High-resolution Blended Analysis of Daily SST and Ice. Global.25°x.25° Daily1981-present None
NOAA Global Surface Temperature (NOAAGlobalTemp) Global5.0°x5.0° Daily1880-presentNone
NOAA Optimum Interpolation (OI) SST V2 Global1.0°x1.0° Monthly,Weekly1981-presentNone
COBE-SST Global1.0°x1.0° Monthly1891-presentNone
COBE-SST2 Sea Surface Temperature Global1.0°x1.0° Monthly1850-2012None
NODC (Levitus) World Ocean Atlas 1994 Global1.0°x1.0° Monthly,AnnualClimoNone
NODC (Levitus) World Ocean Atlas 1998 Global1.0°x1.0° Monthly,AnnualClimoNone

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 Global2.5°x2.5° Daily,Monthly1979-near presentNone
Uninterpolated OLR Global2.5°x2.5° Daily1991-presentNone

Time Series

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.

Region Name Date Range
Multivariate ENSO index: MEITropical Pacific1950-present
Extended Multivariate ENSO index: MEI.extTropical Pacific1871-2005
Nina 1.21870-present
Nina 3 SST 5N-5S,150W-90W1870-present
Nina 3.4 SST 5N-5S,150W-90W1870-present
Nina 4SST 5N-5S,150W-90W1870-present
TNIDifference Nina 1.2 and Nina 41870-present
SOIDifference SP Tahita and Darwin1870-present

Other Datasets

As ENSO impacts weather and climate in general, researchers need to potentially look at all atmosperic and ocean variables. PSD maintains an extensive collection of gridded datasets including our 20th Century Reanalysis(1851=2012). Other dataset can be found from links on PSD's data information webpage. Some other NOAA sites also link to ENSO related datasets: for example,PMEL has an ENSO data source list.

Resources and Additional Information

Using Our Products

You are welcome to use PSD-generated plots — from either a pregenerated figure or an interactive program. We request that you please acknowledge PSD as the source. For example: Image provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their website at http://www.esrl.noaa.gov/psd/.