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Neville Nicholls

Abstract

Canonical correlation is proposed as an exploratory technique for studying teleconnections. It is suggested that the technique can elucidate the temporal signature (i.e., the seasonally varying nature) of the teleconnections and the lags between variables. Several teleconnections studied with the Southern Oscillation are subjected to canonical correlation as examples. The teleconnections studied are between Darwin pressure and Tahiti pressure, southeast Australian rainfall, and Willis Island air temperature. In each example the canonical correlation analysis confirms the teleconnections uncovered previously by other statistical techniques but also suggests the existence of other interesting features of these teleconnections.

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Neville Nicholls

Abstract

The number of tropical cyclones observed in the Australian region during a single cyclone season has ranged from one to nineteen since 1909. Previous studies, using limited data sets, have suggested that interannual variations in the number of cyclones are related to the Southern Oscillation and that an index of the Southern Oscillation (e.g., Darwin pressure) can be used to predict the number of cyclones expected in the coming season. This study uses a 74 year time series of tropical cyclone numbers, from the 1909/10 season to the 1982/83 season to confirm this. Strong and stable correlations are found between cyclone numbers and Darwin pressures before and during the cyclone season. Even stronger relationships are found between Darwin pressure and the number of cyclone days in a cyclone season. The correlations are strong and stable enough to allow prediction of seasonal cyclone activity from several months prior to the start of the tropical cyclone season. A simple equation for predicting seasonal cyclone activity is derived.

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Neville Nicholls

Abstract

Evidence is presented supporting the hypothesis (first expressed over 60 years ago) that interannual fluctuations of early wet season rainfall in the Indonesian Archipelago can be successfully predicted from prior observations of atmospheric pressure anomalies. It is shown that this predictability is related to sea surface temperature anomalies. The postulated mechanism for this predictability is interaction of the atmosphere and ocean leading to a tendency for anomalies in the two media to persist. Experiments to testthis postulate are suggested.

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Neville Nicholls

Abstract

The mouths of October 1971 and 1972 were, respectively, months of heavy and light rainfall over much of Indonesia and New Guinea. The two months also showed considerable differences in the atmospheric circulation in the higher latitudes of the Australian region, with the wetter month (1971) exhibiting stronger westerlies between 30° and 45°S and weaker tropospheric westerlies poleward of 45°S. These changes are similar to those observed in the eastern Pacific during periods of heavy or light equatorial rainfall. Examination of 14 years of data in the Australian region suggests the presence of 1) significant coherence between tropical rainfall and the strength of the subtropical westerlies for periodicities greater than six months with no apparent lag, and 2) a significant out-of-phase relationship between tropical rainfall and high-latitude westerlies at periods greater than 24 months, the latter lagging the former by several months. The relevance of these results to tropical-extratropical interactions and numerical modeling is discussed.

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Neville Nicholls

Abstract

Solutions to a set of differential equations representing a system of postulated interactions between the ocean and the atmosphere can reproduce certain hitherto unexplained aspects of atmospheric and oceanic behavior in the Indonesia-North Australia region. These solutions also represent a biennial oscillation and it is concluded that the postulated air-sea interaction could be the source of the tropospheric quasi-biennial oscillation.

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