Understanding El Niño-Southern
Oscillation (ENSO)
What is ENSO?
ENSO (El Niño-Southern Oscillation) is a natural climate pattern that occurs in the Pacific
Ocean. It involves changes in ocean temperatures and affects weather patterns worldwide.
- El Niño = "The Boy" (refers to warm phase)
- Southern Oscillation = back-and-forth temperature changes in the southern Pacific Ocean
- Location: Mainly occurs in the Pacific Ocean near the equator
The Three Phases of ENSO
1. Neutral Phase
- Trade winds blow from east to west across the Pacific
- Warm water collects in the Western Pacific (near Australia and Indonesia)
- Creates a pattern called "Walker Circulation":
* Warm air rises in the west → Creates rain
* Air cools and dries as it moves east
* Cool, dry air falls near South America
2. El Niño Phase
El Niño is a weather pattern that happens when the Pacific Ocean becomes warmer than usual
near the equator. This happens because the winds that normally push warm water toward
Asia become weaker or stop. As a result, the weather changes around the world.
● More rain and floods in South America (Peru, Ecuador).
● Less rain and droughts in Asia, Australia, and Africa.
● Warmer winters in North America.
● Fewer hurricanes in the Atlantic Ocean.
● Less fish in the Pacific Ocean because warm water stops nutrients from rising.
- Trade winds become weak
● Drought in Australia and Indonesia
● Walker Circulation splits into two parts
3. La Niña Phase
La Niña is the opposite of El Niño. It happens when the Pacific Ocean becomes cooler than
usual because the winds become stronger and push warm water further west.
● More rain and stronger monsoons in Asia and Australia.
● Droughts in South America.
● Colder winters in North America.
● More hurricanes in the Atlantic Ocean.
● More fish in the Pacific Ocean because cold water brings up nutrients.
● Trade winds become stronger than normal
● More warm water pushed toward Western Pacific
● Cold water rises from deep ocean (called thermocline)
- Results in:
* Heavy rains in Western Pacific (Australia, Indonesia)
* Dry conditions in South America
Real-World Effects
- Changes rainfall patterns
- Affects farming and fishing
- Can cause floods in some areas and droughts in others
- Impacts global temperatures
- Influences storm patterns
Fun Facts
- ENSO cycles typically occur every 3-7 years
- The effects can be felt worldwide, not just in the Pacific
- Scientists can predict El Niño and La Niña events several months in advance
- These patterns have been occurring for thousands of years
Key Terms to Remember
- Trade Winds: Winds that blow from east to west near the equator
- Walker Circulation: The normal air circulation pattern over the Pacific
- Thermocline: When cold water rises from deep in the ocean
- Convection: Process where warm air rises and creates clouds/rain
. What are Monsoons?
Monsoons are seasonal winds that bring heavy rain in summer and dry weather in winter.
They mostly affect South Asia, Africa, and Australia.
Types of Monsoons:
1. Summer Monsoon (Rainy Season)
o Happens from June to September.
o Winds blow from the ocean to the land, bringing heavy rain.
o Very important for farming in countries like India, Pakistan, and Bangladesh.
2. Winter Monsoon (Dry Season)
o Happens from October to March.
o Winds blow from land to the ocean, bringing dry weather.
o Can cause droughts in some areas.
How Are They Connected?
● El Niño makes monsoons weaker, causing less rain and droughts.
● La Niña makes monsoons stronger, bringing heavy rain and floods.
● Monsoons affect farming and water supply in many countries.
Remember: ENSO is like a giant see-saw of warm and cold water in the Pacific Ocean
that affects weather patterns around the world!
