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  Seaweek 2003    

Exploring Our Oceans

Oceanography from Space

Investigation 3 - El Nino Southern Oscillation

Examples of Links to Curriculum and Standards Framework II

Biological Science
5.2 Describe interactions between living things and between living things and their non-living surroundings.

Earth Science
4.1 Relate the occurrence of natural events to atmospheric changes and movements of the Earth's crust and mantle.

Physical Science
5.1 Describe the characteristics and applications of the transmission and reflection of energy in the form of heat, light and sound.

El Nino Southern Oscillation

Droughts and bushfires in Australia, floods and storms in the South-western US and Pacific coast, devastating losses in fisheries in South America. How could these events be possibly connected? Peruvian fishermen had long known that around every 5 - 8 years the fish that they normally had in abundance disappeared, along with many of the sea birds from the region which died from lack of food. This occurred around Christmas time so they named the event El Nino that is Spanish for "the Child".

Scientists showed that while this was occurring there were some major changes in the amount of warm water in both the central and eastern Pacific near South America. This pool of warm water replaced the normally cold-water nutrient rich upwellings that provided the start for the rich food chain that led to the fish that the Peruvian fishers depended on. In the western Pacific warm air moves east over the ocean, taking moisture filled air with it. At the same time as their are floods in South America, Australians experience severe drought.

One of the worst major El Nino events in Australia was the summer of the Ash Wednesday bushfires in 1983. In this year a long period of drought and high temperatures caused major bushfires throughout southern and eastern Australia with the loss of many lives. In 1997 another El Nino year saw devastating fires and drought over much of Australia and SouthEast Asia.

The need to be able to predict these devastating changes in our climate has resulted in a major international research program making use of satellites and ocean buoys with temperature sensors to measure changes and make models to warn people to prepare for hard times.
Scientists now believe that these events are caused by a shift in the ocean temperature pushing down the cooler water of the eastern Pacific and altering the climate above the Pacific Ocean. This shift is known as the Southern Oscillation hence the name of the event is known as the El Nino Southern Oscillation or ENSO.

The effects of the El Nino event were widespread in the Pacific basin countries in the summer of 1997 and 1998. In Late 1997 massive bushfires raged in South East Asia and Australia producing a thick blanket of smoke. At the same time torrential rains fell in areas that rarely receive rain such a Peru, California, and some Pacific islands causing massive floods and mudslides.

In the diagram below you can compare the situation in the Pacific in a normal year with an El Nino year.

Obtained from

In the El Nino year a large body of warm water extends down the central and South American coastline stopping the upwellings and flow of nutrients that provide the conditions that support Peru fisheries and coastal wildlife. Moist air builds up over this warmer water and rain falls in the eastern Pacific. In Australia and Asia little moisture-laden air moves over the continents and a drought results from the lack of rainfall.

Measuring the changes in the oceans is carried out by both satellites from overhead as well as from ships or buoys actually in the ocean.

NASA has been directly involved in measuring these changes through the Topex / Poseidon project. This joint US/ French mission uses a highly sensitive altimeter to detect small changes in the surface height of the ocean. While from the surface of the ocean, differences is surface height are imperceptible, over the distance across the Pacific Ocean changes in the height can be measured and interpretation of this data can lead us to a better understanding of the changes occurring during El Nino events.

Activity 1 - Understanding El Nino

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  Investigation 1 - Ocean Surface Temperatures
  Investigation 2 - Phytoplankton Distribution
  Investigation 3 - El Nino Southern Oscillation
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