El Ninomass of warm surface water moving west to

east across equatorial Pacific Ocean

part of larger phenomenon called El Nino – Southern Oscillation (ENSO)

• winds move from areas of highpressure to areas of low pressure

ex: air from balloon exits balloon

normal situation over Pacific Ocean(non-El Nino year):

• low pressure over Asia• high pressure over South America• winds blow east to west• shallow thermocline along South

America, lots of upwelling, cold waterat surface

• deeper thermocline near Asia, warmsurface water piles up

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

sea surface temperature in Pacific Ocean

• El Nino 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 Nino – for the Christ Child

Effects of El Nino

• upwelling along Peru reduced• warm water with few nutrients rises• fisheries decline

Effects of El Nino• increased precipitation over parts of

South America, western andsouthern 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

La Nina• opposite El Nino• swings the other way and winds blow

more than normal towards west