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88 高知論叢　第97号the western Pacific (Southern Oscillation), (iii) ENSO (El Nino Southern Oscillation)basin-wide changes in air-sea interaction in the equatorial Pacific region (Glantz, 1996).Under ....

88 高知論叢　第97号the western Pacific (Southern Oscillation), (iii) ENSO (El Nino Southern Oscillation)basin-wide changes in air-sea interaction in the equatorial Pacific region (Glantz, 1996).Under “normal” conditions, the western part of the Pacific Ocean is warmer thanits eastern counterpart. As a result, air rises high over eastern Indonesia and PapuaNew Guinea, moves east across the Pacific at a high altitude, where it descends andreturns back across the Pacific as westerly winds. When the sea is warmer and the airpressure is lower, large amounts of moist air are lifted up and carried over the landto be released as rain. The result is very high rainfall over large areas of the westernPacific including Indonesia, northern Australia and Papua New Guinea much of thetime. When the eastern Pacific begins to warm up an El Nino event occurs. As the ElNino develops, the western Pacific becomes cooler than the eastern Pacific and thecirculation of air across the Pacific reverses and goes in the opposite direction to usual.These dynamics of ocean and atmosphere are called “the Walker circulation” namedafter Sir Gilbert Walker, a Director-General of British observatories in India who, earlylast century, identified a number of relationships between seasonal climate variations inAsia and the Pacific (Figure 1).Figure 1. Walker circulationsource: http://www.bom.gov.au/climate/glossary/elnino/elnino. shtml