Drought+-Southern+Oscillation+Index

Drought - Southern Oscillation Index

The Southern Oscillation Index graph link below
or [|www.bom.gov.au] and search Southern Oscillation Index graph and archives [] SOI Graph go to paragraph - El Nino then Southern Oscillation Index

The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in air pressure difference between Tahiti and Darwin.

Sustained negative values of the SOI often indicate El Nino episodes. These negative values are usually accompanied by sustained warming of the central and Eastern tropical Pacific Ocean, a decrease in the strength of the Pacific trade winds, and a reduction in rainfall over Eastern and Northern Australia. The most recent strong El Nino was in 1997/98, although it effect of Australia was rather limited. Severe droughts resulted from the weak to moderate El Nino events of 2002/03 and 2006/07.

Positive values of the SOI are associated with Stronger Pacific trade winds and warmer sea temperatures to the north of = Australia, popularly known as a La Nina episode. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that Eastern and Northern Australia will be wetter than normal. The most recent strong La Nina was in 1988/89. A moderate La Nina developed slowly during 2007. =

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