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Ocean · 5 min · 4 steps

El Niño and La Niña

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Goal. Describe what changes in the Pacific during El Niño and La Niña, and read NOAA's index.

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Steps

  1. The temperature of the sea surface, measured from space. The warmest open water is usually in the western Pacific, near Indonesia and the Philippines, piled up there by the trade winds.

  2. Predict

    During El Niño, which part of the tropical Pacific turns unusually warm?

    • The far west, near Indonesia
    • The middle and east, towards South America
    • Only the sea around Taiwan
    Show the answer

    The middle and east, towards South America. The middle and east: when the trade winds weaken, warm water spreads back east.

    The same sea compared with the average for this day in 2003–2014. Red is warmer, blue cooler. The ocean has warmed since then, so look for a band along the equator, east of the date line, that is much redder (El Niño) or bluer (La Niña) than the rest.

  3. Scientists track the Niño 3.4 box. The card shows NOAA's latest reading and every El Niño and La Niña since 1950. Find the biggest red peaks. How does this year compare?

  4. During El Niño, typhoons tend to form farther east, so they cross more warm water and more of them grow very strong. The line marks the 26.5 °C sea they need.

The common mistake

Myth

El Niño is a storm.

Fact. El Niño is a pattern of ocean and wind across the whole tropical Pacific that lasts about a year. It shifts the odds of droughts, floods and typhoons in many places, but it is not one weather event.

Check yourself

Question 1

What happens to the trade winds during El Niño?

  • They weaken
  • They get stronger
  • They reverse every day
Show the answer

They weaken. Weaker trade winds let the warm water flow back east, which weakens the winds further.

Question 2

During El Niño, Indonesia and eastern Australia tend to be…

  • wetter than usual
  • drier than usual
  • much colder
Show the answer

drier than usual. The rainiest area moves east towards the middle of the Pacific, leaving the west drier.

Question 3

NOAA's El Niño index measures the sea temperature…

  • off Taiwan
  • in a box in the middle of the equatorial Pacific
  • near Antarctica
Show the answer

in a box in the middle of the equatorial Pacific. The Niño 3.4 box, from 5° N to 5° S and from 170° W to 120° W.

Words in this lesson

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Curriculum

Taiwan 12-year curriculum (108 課綱), natural science
EIb-Vc-7
US Next Generation Science Standards
MS-ESS2-6 · HS-ESS2-4
England national curriculum
KS3 Geography: weather and climate