Detailed notes explaining the phenomena of El Niño and La Nina including how they form, how they differ from normal conditions, how they impact Africa’s climate and diagrams of their formation for Grade 11 and 12 geography students. These notes also contain questions to test your knowledge about...
El Nino and La Nina
El Niño and La Niña are weather phenomena that occur as a result of interaction between
ocean temperatures and global air circulation. They take place every 6-8 years.
Tropical easterly winds that blow towards LP on equator have an important influence on
Pacific ocean temperatures
- Strong tropical easterlies: water in Eastern Pacific is cold
- Weak tropical easterlies: water in Eastern Pacific is warm
Normal processes
Tropical easterlies blow across Pacific – drag surface water westwards
↓
Upwelling of cold water in Eastern Pacific – nutrients for fish
↓
Cold Peru Humboldt current – flows north along Peruvian coast on west coast of
South America
↓
Cold water is dragged west along equator – heated by tropical conditions – 6°C
warmer than Eastern Pacific
↓
Brings rain to Indonesia and Australia – warm air rises, cools, condenses – LP
↓
Dry on West coast of Peru – subsiding
, El Nino
The temperature of surface waters in eastern Pacific warming
• Occurs at Christmas time every 2-7 years
• Fishing off South America’s west coast is poor – affects economy
• Affects people: when do they plant crops, flooding, drought
Tropical Easterlies weaken
↓
Upwelling of cold water ceases – no more nutrients for fish
↓
Area of warmer water that is usually over western Pacific becomes cooler
↓
Warmer water is displaced eastwards to central Pacific
↓
Normally cold waters of eastern Pacific along South American coast is warmer by 2-
8°C – bad for fishing industry
↓
Normal circulation is altered as a result of changes in Pacific
↓
Convection and rain occurs in eastern and central Pacific
↓
Australia and southern Africa experience drought and cooler conditions – air is
descending
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