Glossary: 20 El Niño and weather words in plain English

News about El Niño is full of jargon. Here are 20 words in plain English, each checked against IMD, NOAA or CPCB.

Ocean words. El Niño is unusual warming of the central and eastern tropical Pacific; La Niña is unusual cooling there; neutral is in between. Together they make ENSO, the El Niño–Southern Oscillation (IMD). Trade winds usually push warm water west; in El Niño they weaken (NOAA). Niño-3.4 is the key Pacific region, and the ONI is its 3-month average temperature departure: +0.5°C or more signals El Niño, and 1.5°C or more counts as strong (IMD). The IOD compares the west and east Indian Ocean; a positive IOD tends to favour monsoon rain (IMD).

Rain words. The LPA is the long-period average rainfall used as "normal". For all-India June–September rain, normal is 96–104% of the LPA and deficient is under 90% (IMD). A rainy day has 2.5 mm or more; heavy rain is 64.5–124.4 mm in a day (IMD Met Glossary).

Heat and air words. In the plains, a heat wave is a maximum of 40°C or more and at least 4.5°C above normal. Red alert means take action. A warm night is when the day reaches 40°C or more and the night stays 4.5°C or more above normal (IMD). The AQI runs from Good (0–50) to Severe (401–500) (CPCB).

This poster is in English only, so the definitions stay exact.

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