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Earth Science
How El Nino Changes Weather Patterns
Pacific warm pool shifts east
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El Nino is a natural climate pattern that begins in the tropical Pacific Ocean and can change weather around the world. During El Nino, warm surface water that is usually piled up near Australia and Indonesia shifts eastward toward Peru and Ecuador. This matters because the ocean and atmosphere work together, so a change in ocean temperature can shift winds, storms, rainfall, and drought patterns far from the Pacific. Scientists track El Nino to help forecast seasonal risks such as floods, dry spells, heat, and changes in winter weather.
Key Facts
- El Nino begins when Pacific trade winds weaken and allow warm surface water to move eastward.
- Normal pattern: strong trade winds push warm water west toward Australia and Indonesia.
- El Nino pattern: warm water spreads east toward Peru and Ecuador, heating the central and eastern Pacific.
- El Nino often brings wetter conditions and flooding risk to coastal Peru and Ecuador.
- El Nino often brings drier conditions and drought risk to Australia and Indonesia.
- El Nino and La Nina are opposite phases of ENSO, and the cycle often repeats every 2 to 7 years.
Vocabulary
- El Nino
- El Nino is the warm phase of a Pacific Ocean climate pattern that changes winds, ocean temperatures, and weather patterns.
- Trade winds
- Trade winds are steady winds near the equator that usually blow from east to west across the tropical Pacific.
- Warm pool
- The warm pool is a region of unusually warm surface water that normally sits in the western tropical Pacific near Indonesia and Australia.
- ENSO
- ENSO stands for El Nino Southern Oscillation, a repeating ocean atmosphere pattern that includes El Nino, La Nina, and neutral conditions.
- La Nina
- La Nina is the cool phase of ENSO, when stronger trade winds push warm water west and cooler water rises in the eastern Pacific.
Common Mistakes to Avoid
- Thinking El Nino is just a local storm is wrong because it is a large ocean atmosphere pattern that lasts for months and affects global weather.
- Assuming El Nino causes the same weather everywhere is wrong because it can bring flooding to some regions while causing drought in others.
- Forgetting the role of trade winds is wrong because weakened trade winds are a key reason warm water can shift eastward across the Pacific.
- Confusing El Nino with La Nina is wrong because El Nino warms the central and eastern Pacific, while La Nina usually cools those waters and strengthens the normal pattern.
Practice Questions
- 1 El Nino events often repeat every 2 to 7 years. If a strong El Nino occurs in 2024, what is the earliest year and latest year another El Nino might occur using this range?
- 2 A student measures sea surface temperature in the eastern Pacific as 24.5 degrees Celsius during neutral conditions and 27.0 degrees Celsius during El Nino. By how many degrees did the surface temperature increase?
- 3 Explain why weakening trade winds can lead to more rain near Peru and Ecuador but more drought risk near Australia and Indonesia.