El Nino: Reading the Wind and the Waves

Image: Sameer Pawar

1. The phenomenon was named El Nino (Spanish for ‘little boy’ or ‘Christ Child’) by South American fishermen in the 17th century. The name represents the time of the year (December, and Christmas) when the phenomenon takes place.

2. El Nino begins in the Pacific Ocean, around the Equator. Usually, winds blow from the Americas towards Asia. This piles up sun-warmed surface water near Asia; near the Americas, colder water from beneath rises to the surface to replace the water that’s pushed away.

3. When El Nino strikes, the winds weaken, and the warm water that was piled up near Asia, slumps back towards the Americas; cold water near the Americas does not rise to the surface, and a whole lot of warm water collects there.

4. Warm waters weaken the winds; this makes the water warmer; this makes the winds weaker; this makes the water warmer still… This cycle makes El Nino grow stronger.

5. So, what happens to this mass of warm water? It moves towards Asia in the form of large (hundreds of miles wide), slow waves (Rossby waves), which start deep below the surface and take months to reach Asia. Once it reaches, the waves bounce back towards the Americas.

6. El Nino causes winter rains and floods in the southeastern US, and drought in Asia and Australia. The low air pressure over the warm Pacific can also disrupt the formation of a nascent monsoon in the Indian Ocean. It does not guarantee these conditions, but makes them more likely.  

7. Scientists are yet to entirely decipher this pesky phenomenon; for instance, why or when it happens, or predict its intensity.

8. And then there is El Nino’s counterpart, La Nina. But let’s leave that for another day.