The El Nino, La Nina See-saw
The Age
Monday March 19, 2007
THE BEST WAY TO UNDERSTAND El Nino and La Nina events is to picture a see-saw in a playground. When one side goes up the other side goes down.
During El Nino, there's high air pressure over the western Pacific (Indonesia, and Australia) and low air pressure over the central and eastern Pacific (South America.) Warm water from the western Pacific flows to the east Pacific during an El Ni?o, taking rain with it. As a result, normally dry desert areas in countries like Peru experience flooding. Meanwhile, countries in the western Pacific - like Australia - experience dry drought conditions and sometimes increased bushfires.An El Nino episode finished this month.During La Nina the opposite happens. Air pressure is low over Australia and strong winds - known as trade winds - send warm water west towards northern Australia. As a result, eastern and northern Australia experience wetter than normal conditions.Historically, El Nino and La Nina last for a year or two and occur irregularly with intervals of two or seven years.El Ni?o and La Ni?a are grouped under the term ENSO (El Nino Southern Oscillation).ENSO measures the see-saw pattern of fluctuating surface air pressure between the eastern and western tropical Pacific Ocean.Scientists are debating whether global warming affects the frequency or duration of El Ni?os and La Ni?a events.-- LISA MARTIN www.bom.gov.au/climate/enso/ The most recent El Nino episodes occurred in 1872-73, 1982-83, 1986-87, 1991-92, 1993, 1994, 1997-98, 2002-03, and 2006-07.La Nina events occurred most recently in 1950, 1954-55-56, 1964, 1971, 1973-74-75, 1988-89, 1995-96, and 1998-99-2000.
© 2007 The Age
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