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Different Amounts of Rain at Different TimesPlease wait for the files to download. This may take a minute depending on the speed of your modem.Don't hit reload or stop until all the files are downloaded. |
The Graphs |
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El Niño |
Normal Conditions |
La Niña |
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The graphs above are called distribution curves. The shape of these curves will actually vary from location to location around Australia but the ones shown here represent typical rainfall distributions for many parts of the country. They show how often (the frequency) a location receives either low, normal or high rainfall during each phase of the climate i.e. El Niņo, Normal and La Niņa. As the climate system cycles through these phases the "normal" rainfall distribution tends to shift toward "dry" during El Niņo and toward "wet" during La Niņa. For example The rainfall distribution
curves can be used to calculate the probabilities of receiving each
of the rainfall categories. The Bureau uses such probabilities to forecast
rainfall for the season ahead click on the following link to see the
current Seasonal
Climate Outlook for the next 3 months. |
The Pie Charts |
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The graphed probabilities (see above) can be represented as proportions of a pie chart. During "normal" conditions there are equal proportions for each of the rainfall categories. During El Niņo conditions the "dry" category is largest, while during La Niņa the "wet" category is largest. The proportions in each rainfall category will actually depend on the strength of the El Niņo or La Niņa event and will also differ from location to location and from season to season. The pie charts below show typical proportions for each phase of the climate. Spin the pie charts by moving your mouse over and off each one and see how often you receive each of the rainfall categories. |
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El Niño Year (strong negative *SOI value) |
Normal Year (SOI close to zero) |
La Niña Year (strong positive SOI value) |
Move your mouse over and off a pie chart to spin.The pie charts should spin and stop at random. If they don't spin then your web browser may not be able to use the javascript involved. You could print off this page and cut out the pie charts. Insert a tooth pick through the centre of the chart to make a top. Spin the top to get a result. |
| Each time the Normal
pie chart spins and stops, there is an equal chance of landing on any
of the three segments. However each time the El Niño or La
Niña charts spin, the chances of landing on any segment differ.
See below for the chances (probabilities). |
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El Niño |
Normal |
La Niña |
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Wet
= 17% |
Wet
= 33.3%
(1 in 3 chance) Dry = 33.3% (1 in 3 chance) Normal = 33.3% (1 in 3 chance) |
Wet
= 50%
(approx. 1 in 2 chance) Dry = 17% (approx. 1 in 6 chance) Normal = 33% (approx. 1 in 3 chance) |
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Please
note
As well as rainfall, scientists also study sea surface temperatures, height, strength and direction of trade winds and the position of rain clouds in the tropical pacific region of the world, when they define El Niño or La Niña events. Then they make graphs to show which event is affecting us. *See the SOI graph. SOI stands for Southern Oscillation Index. Southern Oscillation Index (SOI) definition. |
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