1. mass of warm surface water moving west to
east across equatorial Pacific Ocean
part of larger phenomenon called El Niño –
Southern Oscillation (ENSO)

2. • El Niño occurs every 3 to 8 years
• Usually lasts about 1 year
• Scientists do not know why pressure
changes causing winds to shift
• Warm water arrives at South America
around Christmas – hence El Niño –
for the Christ Child

3. NORMAL SITUATION OVER PACIFIC
OCEAN
(NON-El Niño YEAR)
• Low pressure over Asia
• High pressure over South America
• Winds blow east to west
• Shallow thermocline along South
America, lots of upwelling, cold water
at surface
• Deeper thermocline near Asia, warm
surface water piles up

5. EL NINO YEARS OVER PACIFIC
OCEAN:
• Pressure change = Southern Oscillation
• Higher pressure over Asia
• Lower pressure over South America
• Winds weaken or blow west to east
• Thermocline deepens along South
America, little upwelling, warmer
water at surface
• Warm surface water sloshes back along
equatorial Pacific

8. SEA SURFACE TEMPERATURE IN
PACIFIC OCEAN

9. EFFECTS OF EL NINO
• upwelling along Peru reduced
• warm water with few nutrients rises
• fisheries decline

10. EFFECTS OF EL NINO
• increased precipitation over parts of
South America, western and
southern U.S.
• can result in severe flooding
• drought in Australia, Indonesia,
Phillipenes
• reduction in annual monsoons in India
• can result in severe crop damage
• severe property damage and thousands
of deaths