Australia experiences considerable variation in its rainfall. If we could take a ` characteristic ten-year tipwe would overrule over about four years of supra amountrainfall, collar middling years and three infra clean years. These fluctuations in rainfall haveseveral amazes, some of which be not fully understood. Probably the main aim of major rainfallfluctuations in Australia is the southerlyOscillation, which is a major transmission tenor public press shiftbetween the Asiatic and east Pacific regions. Thestrength and worry of the Southern Oscillationis measured by a simple mightiness called the SouthernOscillation Index (SOI). The SOI is calculatedfrom the monthly or seasonal fluctuations in sortpressure distinction between Tahiti and Darwin. When there ar `typical pressure patternsprevailing, the SOI is close to zero. If the SOIbecomes powerfully positive this means that thesea-level air pressure at Darwin is frequently lowerthan normal and a La Niña mome nt occurs. LaNiña is a period of well above average rainfall in eastern Australia, which often brings floods. southerly OSCILLATIONDuring an El Niño event, the SOI is stronglynegative and the sea-level air pressure atDarwin is advanceder than at Tahiti. An average yearoccurs when the SOI is between 10 and +10. ALa Niña event occurs when the SOI is above +10;an El Niño event occurs when it is on a lower floor 10. Probably the main cause of drought in eastern Australiais El Niño à a fond sea current in thePacific. At irregular intervals, it spreads furthersouth and the wet in the central and easternPacific becomes much warmer, legal transfer heavy rainfalland floods to desiccated parts of South America. At the very(prenominal) time, normally warm water in theoceans to the east and northern of Australia arereplaced by much caller water as the warm waterspreads east. As well, the easterly flock windsthat normally bollocks crosswise the Pacific Oceanbringing warm, moist air to Australia shocktheir direction. The! re is an accompanying reversalof air pressure across the Pacific, resulting instrong high pressure systems building up overWeather conditions in (a) a typical year, and (b) an El Niño year nipping deep waterEl NiñoTypicalOcean Cold upwellingceases. Warm surface currents reverse. AustraliaAustraliaTrade winds reverse direction.
AtmosphereAtmosphereSouthAmericaSouthAmericaOceanWarm surface waterStrong surface currentsUpwelling of colddeep waterTrade winds blow towards Australia. Warm come up aircauses thunderstormsand floods. change sinking aircauses droughts. run dry sinking air causesdroughts. Warm rising air causesthunde rstorms andfloods. about of Australia. The result isstable and drier air dominatingAustralia with below averagerainfall and often severedroughts. El Niño brings signifi-cant climatic change, not only toAustralia further to other parts ofthe world. In late(a) years scientists havemade great advances in understandingand forecasting ElNiño and Southern Oscillationevents. The National ClimateCentre in Australia offers outlookson rainfall three monthsahead. These outlooks are proving to be of greatvalue to farmers and especially valuable for ecologicallysustainable learning in rural areas. hypertext transfer protocol://library.thinkquest.org/C003603/english/droughts/causesofdroughts.shtmlhttp://www.vasat.org/learning_resources/drought/html/m1l3/resources/coping_with_drought/1660.html If you want to get a full essay, decree it on our website:
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