What is El Niño?

El Niño occurs in the South pacific ocean between Australia/Indonesia and South America.
It is a disturbance of the normal balance between oceanic and atmospheric components of the climate. How do these disruptions occur?

Firstly, think about the answers to these questions:

Q

Which contains more energy, a bath full of warm water or a kettle full of boiling water?

A

The answer is probably the bath, although it does depend on the temperature of the water.

Q

How long does it takes for a beaker full of boiled water to cool down?

A

It takes a long time, but it depends mainly on the volume of the water.

Q

Which is more dense, hot water or cold water?

A

Warmer water will always float on top of the colder water.

The ocean waters are huge reserves of thermal energy and are a major influence on the world’s climate. The waters obey some of the simple ideas illustrated above.

How does El Niño work?

Normal conditions
During El Niño

Under normal conditions (above left), reliable winds blow from South America, westwards across the Pacific Ocean, towards southern Asia and Australia. This causes the water to heap up on the western side, so that the sea level is 0.5metres higher! As the warmer water is water is shifted, cooler water rises to replace it. This water is rich in nutrients from the ocean’s bottom.

During El Niño (above right) the winds become weaker, resulting in the warm water layer in the west becoming shallower and creating a deeper warm water layer in the east. This prevents the upwelling of the cooler water and nutrients off the South American coast, and affects the food chain.

Why is El Niño significant?

  • The upwelling of the cool water is switched off, the supply of nutrients for food chains is decreased. The consequence of this is to reduce the productivity of the area, so there are fewer phytoplankton [small plants] and a smaller biomass for animal life. An economic consequence is that the fish stocks are reduced.
  • The name El Niño means the Little Boy or Christ Child in Spanish. It was used because the event often occurred around Christmas time. Fishermen recognised it from the appearance of warmer than usual water which they could link with the prediction of reduced catches later in the year.
  • As the energy focus is shifted eastward, the rainfall in the west is reduced. This affects both continents, Australia and Indonesia can experience severe drought and forest fires. In South Afica, Peru may experience severe rainfall and flooding.
  • On a wider scale, the influence of such a large shift in one component of the climatic system, can be felt beyond the immediate vicinity of the South Pacific.


Predicting El Niño

Scientists are constantly gathering data of the water temperature from the sea in order to try to predict an El Nino event. This is done using a series of floating sensors called the TAO Array - each sensor is fixed to a moored buoy so that its position is known.

You can find the outcomes of gathered data and an animation of an El Niño at the following web site:
http://www.pmel.noaa.gov/tao/elnino/nino-home.html



Find out more about the oceans:

Waves
Salty oceans
Oceanic conveyor belt
The El Niño effect

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February 2007