6.5 - El Nino

ENSO

El Nino Southern Oscillationand

La Nina

Key Info.• It is when ocean surface temperature fluctuates

significantly from the norm• El Nino = higher than normal, La Nina = lower;

sustained anomalies of greater than 0,5 ºC are required

• It occurs in the eastern Pacific Ocean off the coast of S. America

• It usually takes place around Christmas time• The recurrence interval is 2-7 years• ENSO is associated with floods, drought and other

disturbances; its impact can be global• The most recent occurrence started in September

2006 and lasted until early 2007

The Walker Cell - Normal

South Pacific Gyre

El Nino Conditions

El Nino Temperature

Anomaly

La Nina – What’s the difference?

La Nina Temperature Anomaly

Normal

El Nino

La Nina

But what actually causes these

fluctuations from the norm?

Impacts of El Nino• The impact of El Nino is felt most significantly and directly

along the western coast of S. America (Peru, Ecuador); in particular increased thunderstorm activity and heavy rainfall leading to flooding and landslides.

• El Nino can have far reaching impacts due to teleconnections – e.g. drier and hotter conditions over Amazon Basin, drought in Australia and Southeast Asia, wetter and colder winters in southern California and northern Mexico.

• El Nino does not only affect climate, other significant impacts include changes in sea nutrient levels as warm nutrient poor waters flow in from the eastern Pacific replacing the nutrient rich upwelling usually found along the western coast of South America.

• La Nina generally leads to the opposite impacts of El Nino.

Major Episodes

• 1982-3 and 1997-8 stand out in recent history as major El Nino events

• During the ’97-8 episode air temperature increased by 1.5 ºC compared to the usual increase of 0.25 ºC

• Extensive flooding took place in Peru and Ecuador with significant impacts on life, property and economies