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Historical Occurrence of El Nino and its Impact on Food Crop Production at a Regional Level in Asia and the Pacific 89The Southern Oscillation is a seesaw like oscillation of sea level air pressurecha....

Historical Occurrence of El Nino and its Impact on Food Crop Production at a Regional Level in Asia and the Pacific 89The Southern Oscillation is a seesaw like oscillation of sea level air pressurechange across the Pacific basin. Southern Oscillation Index (SOI) is the normalizeddifference in pressure between Tahiti (south-central Pacific) and Darwin (northernAustralia) (Tahiti minus Darwin). The combination of El Nino, the oceanic component,and the Southern Oscillation, the atmospheric component, makes up the term ENSO.Negative SOI is associated with warm ENSO and positive with cold ENSO, whichis referred to as La Nina, the young girl in Spanish. As shown in Figure 2, El Nino of1997/98 was clearly evidenced by rapid fall and continuous large negative value of SOI.Figure 2. Southern Oscillation Index 1997-2002source: http://www.bom.gov.au/climate/glossary/elnino/The ENSO system arouses keen interest for three reasons: it can be modelled, itsinfluence on climate is global, and there is a time lag between climatic consequences(Gommes et al., 1998). During the months of April-September, the ENSO warmevent has been associated with drought in Indonesia, northern Australia, India andnortheastern Latin America, while its expected impacts in October-March are droughtin southern Africa, continuing drought in northern Australia and Indonesia, high rainfallin eastern equatorial Africa, the Gulf of Mexico, western equatorial Latin America