EL NINO & LA NINA (ENSO)
Geography
1. INTRODUCTION
El Niño and La Niña are climate patterns in the Pacific Ocean that affect weather worldwide.
They are the warm and cool phases of a recurring climate pattern across the tropical Pacific Ocean.
This whole system is called ENSO – El Niño Southern Oscillation.
ENSO has three phases:
• El Niño – Warming phase
• La Niña – Cooling phase
• Neutral phase – Normal condition
ENSO strongly influences:
• Indian Monsoon
• Global rainfall pattern
• Droughts and floods
• Agriculture and food prices
• Cyclones and hurricanes
2. WALKER CIRCULATION
Walker circulation is the east-west (zonal) air circulation in the tropical Pacific Ocean.
Normally:
• Warm water accumulates near Indonesia and Australia.
• Air rises over warm western Pacific.
• Air moves eastward in upper atmosphere.
• Air descends over eastern Pacific (Peru coast).
• Trade winds blow from east to west along the equator.
This circulation causes:
• Heavy rainfall in western Pacific (Indonesia region)
• Upwelling of cold water near Peru coast
• Rich fishing grounds due to nutrient-rich cold water
Any disturbance in this circulation leads to El Niño or La Niña.
3. EL NINO SOUTHERN OSCILLATION (ENSO)
ENSO is a periodic fluctuation in:
• Sea Surface Temperature (SST)
• Atmospheric pressure
• Trade wind strength
It occurs every 3 to 7 years.
Temperature change: 1°C to 3°C above or below normal.
ENSO phases:
• El Niño – Warming of central and eastern Pacific
• La Niña – Cooling of central and eastern Pacific
• Neutral – Near normal condition
4. EL NINO
Meaning:
El Niño is the abnormal warming of sea surface temperature in the central and eastern Pacific Ocean.
Ocean Conditions:
• Trade winds become weak or reverse
• Warm water moves towards Peru coast
• Upwelling of cold Humboldt current stops
• Sea surface temperature increases
Atmospheric Conditions:
• Walker circulation weakens
• Rainfall decreases in Indonesia, Australia, India
• Rainfall increases in Peru, Ecuador, central Pacific
Effects:
• Drought in India, Indonesia, Australia
• Floods in South America
• Poor monsoon in India
• Fall in agricultural production
• Increase in food inflation
• Forest fires in Australia
• Fewer cyclones in Atlantic, more in Pacific
Impact on India:
• Weak monsoon
• Drought conditions
• Crop loss
• Higher food prices
• Stress on economy
5. LA NINA
Meaning:
La Niña is the abnormal cooling of sea surface temperature in the central and eastern Pacific Ocean.
Ocean Conditions:
• Trade winds become stronger than normal
• More warm water pushed towards western Pacific
• Strong upwelling of cold water near Peru coast
• Sea surface temperature falls below normal
Atmospheric Conditions:
• Walker circulation becomes stronger
• Heavy rainfall in Indonesia, India
• Drier conditions in eastern Pacific
Effects:
• Good monsoon in India
• Floods in India and Southeast Asia
• Better agricultural output
• More cyclones in Atlantic
• Colder winters in some regions
Impact on India:
• Strong monsoon
• Flood risk
• Better crop yield
• Improved rural economy
6. ENSO NEUTRAL
Meaning:
• Neither El Niño nor La Niña
• Sea surface temperature remains near normal
• Walker circulation remains normal
Sometimes:
• Ocean indicates El Niño but atmosphere does not respond (or vice versa)
7. COMPARISON: EL NINO VS LA NINA
El Nino:
• Ocean warms
• Trade winds weaken
• Upwelling reduces
• Weak Indian monsoon
• Drought in India
La Nina:
• Ocean cools
• Trade winds strengthen
• Upwelling increases
• Strong Indian monsoon
• Floods in India
8. IMPORTANCE FOR INDIAN MONSOON
Indian Monsoon depends heavily on ENSO:
• El Niño year = weak monsoon (generally)
• La Niña year = strong monsoon (generally)
IMD uses ENSO status for:
• Monsoon forecasting
• Crop planning
• Water management
• Disaster preparedness
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Subject: Geography
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