EDITOR'S NOTE: The best way to use this special section on climate prediction, featuring the Southern Oscillation Index (SOI) system, is to read the glossary of terms first. The forecaster's shorthand of referring to SOI and ENSO (El Niño/Southern Oscillation) can be confusing to the lay person. For the sake of simplicity, we stick with SOI phases as our basic climate pattern reference. Information and graphics supplied by the Queensland Centre for Climate Applications.
GLOSSARY OF TERMS
SOI — SouthSern Oscillation Index. A convenient measure of the integrated ocean and atmospheric conditions in the Pacific.
SOI phases — The level and change in SOI over two months. Certain SOI phase conditions are associated with above-average or below-average future rainfall patterns, particularly in Australia, but also in other parts of the world.
SST — Sea-Surface Temperature. Small changes in SST can lead to big changes in climate patterns. SST changes in the Pacific lead to changes in the SOI.
El Niño — SST changes in the Pacific characterised by warmer than normal water off the South American coast and cooler water around Australia. Frequently associated with below-median rainfall in Australia but above-median rainfall in South America.
La Niña — SST changes in the Pacific characterised by cooler than normal water off the South American coast and warmer water around Australia. Less frequent than El Niño, and often associated with above-median rainfall patterns in Australia.
ENSO — El Niño/Southern Oscillation. The combined effect of SST changes and corresponding changes in the atmosphere as measured by the SOI. It is this interaction of ocean and atmosphere that leads to changes in the rainfall pattern.
Normal rainfall - An Australian myth. Australia has the highest rainfall variability in the world. It could be defined as the long-term average, but because of the extreme variability, this hardly ever occurs.
Average — The total amount of something, rainfall or yield received over a number of years and divided by the number of years that make up the record. In a perfect or 'normal' distribution median and average are the same. Rainfall is rarely normally distributed.
Median — Could be called 'half-way' point. It measures the amount of rainfall or yield that is exceeded in 50 per cent of years. It is often more meaningful than average, because it is not sensitive to extreme values.