Abstract
THE ‘Southern Oscillation’, as statistically defined by Sir Gilbert Walker, is the barometrically recorded exchange of air mass in tropical latitudes around the complete circumference of the globe1,2. Indices of Southern Oscillation based on the surface pressure differences between the Indonesian equatorial low (measured at Darwin, Australia) and the South Pacific subtropical high (considered the Southern Oscillation's eastern core and measured at Easter Island) have been used by Quinn3–5, who relates fluctuations in these indices to anomalous equatorial rainfall and occurrences of ‘El Nino’, (the accumulation of anomalously warm water in the eastern tropical Pacific). In this paper, we use 12-month running means of monthly mean surface pressures over three areas across the northern tropical Pacific as an index of the Southern Oscillation index, and we find that pressure convergences in this index are associated with years of relatively low numbers of western Pacific tropical cyclones.
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