El NiñoEl Niño

What is El Niño?What is El Niño?What is El Niño?What is El Niño?• A shift in ocean current direction and water

temperature• El Niño: the ocean part: Warm phase of ENSO:

El Niño - Southern Oscillation• Southern Oscillation: the atmospheric part;

a global wave pattern• La Niña: is the cold phase of ENSO:

Cool sea temperatures in tropical Pacific

• EN events occur about every 3-7 years

Effects of El NiñoEl Niño• Normally, cold water rises up the shore of

South America and brings fish food.

• El Nino brings warm water and the current sinks near S.A.

• A shortage of fish food means less fish for fishermen and the rest of the population.

• The warm water also brings rain to Peru.

• Australia has a cold current now and drought is produced.

Peak El Niño occurs about Christmas

season ...• ““Christ Child”Christ Child”• ““The Boy”The Boy”• ““The Little The Little

One”One”

• Cf: La NiñaCf: La Niña• ““The Girl”The Girl”

WarmCold

Warm Cold

(2) Warm water heats the atmosphere, the air rises, and low-level trade winds converge toward the warm water. Subsiding air occurs in the eastern Pacific basin. December-February Average

Conditions

(2) Warm water heats the atmosphere, the air rises, and low-level trade winds converge toward the warm water. Subsiding air occurs in the eastern Pacific basin.

Winds and Sea Surface Temperature are COUPLED. The SSTs influence the winds and vice versa.

(1) Easterly trade-winds help push warm water to the western Pacific and upwell cold water along the equator in the eastern Pacific Ocean.

• Easterly trade winds weaken

• Thermocline deepens and the cold water upwelling decreases in the eastern Pacific.

• Convection shifts eastward over the central and/or eastern Pacific Ocean. Convection becomes suppressed over the far western Pacific/ Indonesia.

ENSO ImpactsOccur around the worldDroughts (e.g. Australia, Africa, Brazil, Indonesia)Floods (e.g. Peru, southern USA)

The drought of 1988: cost about $40 billion

Star Tribune Aug 2 1993 Minneapolis, MN

FLOODSUpper MississippiBasin

Source: Trenberth

El Niño and Global warmingEl Niño and Global warming

1998 warmest year on record, 2001 second warmestEl Niño contributes to global warmingEl Niño contributes to global warming

There is a pattern of more and bigger El Niños in past 20 years

El Niño years

La Niña years

Is global warming contributing to changes in El Niño?Likely, yes, to some extent.Which part is natural variability?