El Niño Southern Oscillation (ENSO)

Normal Conditions:
El Niño:

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El Niño Classroom Poster
link to El Nino poster
Click image to download pdf of poster with activity.

ENSO 101


Some Basics

What is El Niño/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 El Niño/Southern Oscillation (ENSO) basically refers to both the El Niño and La Niña phenomena together. See more detailed information about 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 two to seven 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. 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.

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