Tropical-Extratropical Interactions in the Australian Region

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  • 1 Australian Numerical Meteorology Research Centre, Melbourne, Victoria, Australia
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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.

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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