Southern Oscillation
Use this diagram to show the effect of moving averages on a time series with sizeable random fluctuations.
Initially the diagram only allows moving averages of odd order. Click the controller to adjust the number of values being averaged.
Even run lengths
The diagram can also display centred moving averages with even run lengths.
Ordinary moving averages with even run length give smoothed values half-way between the times of the values in the original data. A subsequent stage of moving averages of pairs of values centres them. This is equivalent to defining a 4-point moving average as:
The Southern Oscillation Index is defined as the barometric pressure difference between Tahiti and the Darwin Islands at sea level. The southern oscillation is a predictor of El Nino which in turn is thought to be a driver of world-wide weather. Specifically, repeated southern oscillation values less than -1 typically defines an El Nino. The time series plot shows the index between January 1984 and December 1987.