El Niño – Southern Oscillation
Climate Impact on Australia with Extreme Droughts and Major Flooding
Nov 9, 2007
The Pacific Ocean Creates Extremes
El Niño is described as an extreme interaction of the ocean and atmosphere as part of the Southern Oscillation. The Southern Oscillation happens in the Pacific Ocean between Asia and South America. Because of the vast expanse of the Pacific Ocean, it creates and controls the climate, specifically the large-scale interactions between the atmosphere and the ocean. With other oceans and seas, land and water temperatures affect the atmospheric circulation. As these bodies of water are smaller, the land tends to take away from the ocean and atmosphere interaction. In the Pacific, these major interactions are essential in creating El Niño – Southern Oscillation, or ENSO.
Walker Circulation Explains Typical Air Circulation in Pacific
The Walker Circulation model, developed by the British climatologist Gilbert Walker last century, explains the typical Pacific Ocean air circulation occurrence. The Walker Circulation depicts an east to west circulation. These easterly trade winds bring warm moist air to the region around Indonesia and Australia. There, rainfall is high and moist air occurs. Then, the air travels to the east, drying out, eventually reaching South America, specifically Peru. There, the air is cool and dry. This is the typical flow of air over the South Pacific.
What is El Niño - Southern Oscillation?
Fluctuations in the Walker Circulation are called the Southern Oscillation. These are described as changes in the average atmospheric pressure between the mid-Pacific and Northern Australia. It is a major air pressure shift. These are measured by the Southern Oscillation Index (SOI), which calculates the differences in atmospheric pressure between Tahiti and Darwin, Australia. Major fluctuations in the SOI indicate whether El Niño or La Niña is in effect. When the SOI is negative, El Niño is happening or when it is positive, La Niña is in effect. Australia's Bureau of Meteorology monitors and keeps up-to-date information on the current El Niño - Southern Oscillation status.
The most extreme events or changes of the Southern Oscillation are known as El Niño. These events pose as a major influence on the climate in Australia. The effects of El Niño have been observed in Australia since 1791. These events lead to a highly variable climate, with extreme drought or high rainfall resulting in flooding.
El Niño/ La Niña Impact in Australia and the World
- El Niño is a natural and normal part of the climate in the Pacific region. Each El Niño or La Niña is unique in characteristic and strength, and do not have a uniform effect on Australia. El Niño causes very dry conditions, to extreme droughts. On the other hand, La Niña means wetter conditions with flooding.
- El Niño happens when there is higher atmospheric pressure over Australia and the Indian Ocean and lower over the SE Pacific. La Niña conditions result from the reverse.
- El Niño is caused by weakened or non-existent trade winds, causing ocean temperatures to rise. La Niña is caused by harder trade winds, resulting in cooler ocean temperatures near Australia.
- El Niño happens every 3-8 years. These events usually begin in March to June. Then the major events happen at the end of the year. El Niño means “Christ”, first noted by the Peruvians, as El Niño weather events tended to happen near Christmas.
- As it is not a regular event, El Niño is difficult to predict. It takes several months of SOI data reflecting major changes to detect El Niño. El Niño cannot be predicted but once El Niño is detected, its length and effects can be forecasted. El Niño cannot be prevented but only better understood and better forecasted by meteorologists.
- El Niño affects the weather all over the world, yet originates only in the tropical Pacific Ocean.
- Australia is currently experiencing the effects of La Niña, with colder temperatures and more rainfall than usual. Yet this La Niña is weaker than historically experienced. In 2000, Australia experienced the 2nd wettest year on record, nationally.
- 1982-83 and 1997-98 were two of the most extreme El Niño events recorded, effecting regions around the world.
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