Spatial and temporal variations of the Southern Oscillation

Abstract The Southern Oscillation is an important mode of operation of the atmosphere. Several indices of the Southern Oscillation have been recognized, but for many purposes an index that gives a continuous, homogeneous time series is required. Phase differences between various areas complicate the definition of a simple index but weighted values of seasonal surface pressure at Darwin and Tahiti seem suitable for reference purposes. Time series of short period correlation coefficients prove useful for revealing temporal variations in the character and amplitude of the Southern Oscillation and reveal times when it is not very prominent. Lag relationships are determined and used to indicate some aspects of the circulation near times of phase reversal of the oscillation. Spectral analysis showed most variance to be in the range of 2 to 10 year periodicities, and cross spectral calculations further indicated that only for the 2–10 year range, and mainly for the 3–6 year range, of periodicities is there large‐scale coherence and out‐of‐phase relationships between stations in the South Pacific and Darwin. This defines the time scale of the Southern Oscillation. The Southern Oscillation is not confined to tropical and subtropical latitudes but is clearly linked to mid‐latitude systems and long waves in the westerlies. East‐west circulations coupling the South Pacific Convergence Zone and the South Pacific high also appear to play an important role in the Southern Oscillation.