El Niño basics and science
What El Niño is, how it is measured, and how it can change the Indian monsoon. Plain language, with the agency names next to the claims.
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- Normal conditions: what a balanced Pacific looks like
To understand El Niño, it helps to know what a normal year looks like across the tropical Pacific Ocean.
- El Niño explained in one picture
El Niño is a natural pattern in the tropical Pacific Ocean that usually returns every two to seven years.
- La Niña vs El Niño vs neutral: the three ENSO phases side by side
The El Niño–Southern Oscillation (ENSO) is a natural cycle in the tropical Pacific with three phases.
- What the Niño-3.4 box is and why everyone measures it
When you read that El Niño is "+2. 1°C", that number almost always comes from one patch of ocean: the Niño-3.
- The Southern Oscillation: the air-pressure see-saw behind El Niño
El Niño is half of a pair. The "Southern Oscillation" is the other half: a see-saw in air pressure across the tropical Pacific.
- How a Pacific ocean pattern changes India's monsoon winds
How can warm water in the middle of the Pacific Ocean change the monsoon over India?
- Thermocline and upwelling: the hidden ocean layer that drives El Niño
Most El Niño maps show the sea surface. But the key change happens tens of metres down, at a boundary called the thermocline.
- Watch, Advisory, Final: how NOAA's El Niño alert system works
News reports often say NOAA has issued an "El Niño Advisory". Here is what the labels in NOAA's ENSO Alert System mean, using the Climate Prediction Center's (CPC) own definitions.
- Weak, moderate, strong, ‘super’: what the El Niño strength labels mean
Headlines call El Niño "strong", "very strong" or even "super". Here is what the official labels mean.
- The Indian Ocean Dipole: India's other ocean see-saw
El Niño gets the headlines, but India's monsoon also listens to its own ocean. The Indian Ocean Dipole (IOD) is a see-saw in sea temperature between the western and eastern Indian Ocean.
- Why El Niño releases ocean heat rather than creating new heat
El Niño years often bring record heat. That can make it sound as if El Niño creates heat.
- How forecasters predict El Niño months ahead: models, buoys and satellites
Agencies talked about this El Niño months before it arrived. How do they see it coming?