PERSISTENCE CHARACTERISTICS OF AUSTRALIAN RAINFALL ANOMALIES

Using 79 years (1913-1991) of Australian monthly precipitation data we examined the nature of the persistence of rainfall anomalies. Analyse s were performed for four climate regions covering the country, as wel l as for the entire Australian continent. We show that rainfall over t hese regions has high temporal variability and that annual rainfall am ounts over all five sectors vary in phase and are, with the exception of the north-west region, significantly correlated with the Southern O scillation Index (SOI). These relationships were particularly strong d uring the spring season. It is demonstrated that Australian rainfall e xhibits statistically significant persistence on monthly, seasonal, an d (to a limited extent) annual time-scales, up to lags of 3 months and one season and 1 year. The persistence showed strong seasonal depende nce, with each of the five regions showing memory out to 4 or 5 months from winter and spring. Many aspects of climate in the Australasian r egion are known to have undergone considerable changes about 1950. We show this to be true for persistence also; its characteristics identif ied for the entire record were present during the 1951-1980 period, bu t virtually disappeared in the previous 30-year period. Much of the se asonal distribution of rainfall persistence on monthly time-scales, pa rticularly in the east, is due to the influence of the SOI. However, m ost of the persistence identified in winter and spring in the north-we st is independent of the ENSO phenomenon. Rainfall anomalies following extreme 'dry' and 'wet' months, seasons and years (lowest and highest two deciles) persisted more than would be expected by chance. For mon thly extreme events this was more marked in the winter semester for th e 'wet events', except in the south-east region. In general, less pers istence was found for the extreme seasons. Although the persistence of dry years was less than would have been expected by chance, the wet y ears appear to display persistence. (C) 1997 by the Royal Meteorologic al Society.