25 May 2007

MEDIA RELEASE

Walker circulation weakens to record levels

Australian climate scientists are investigating changes in the El Niño, tropical climate and one of the planet’s most important atmospheric systems – the Walker circulation.

In research published in the latest edition of Geophysical Research Letters scientists from the Bureau of Meteorology and the CSIRO have confirmed that since 1977 changes in the tropical atmosphere and ocean reached record levels.

The Southern Oscillation Index (SOI) (an index used to track the El Niño – Southern Oscillation (ENSO) phenomenon) has never been lower and the trade winds have never been weaker, while tropical ocean surface temperatures and air pressure recorded over northern Australia have never been higher in the observed climate record.

The changes reflect a record weakening of the Walker Circulation – one of the largest and most important atmospheric wind systems in the world. Changes in the Walker Circulation are known to increase the risk of drought, flood and agricultural production in many countries – including Australia.

Writing in the latest edition of Geophysical Research Letters, Dr Scott Power from the Bureau of Meteorology and Dr Ian Smith from CSIRO suggest that ENSO values have actually shifted to lower mean values.

“El Nino activity only seems very high if climate is assumed to be the same now as it was 50 years ago. It isn't. ENSO is now driving climate variability about new climatic averages” said Dr Power.

“While concerning, taking these changes into account has the potential to unlock more accurate seasonal climate forecasts.”

For their research Dr Power and Dr Smith examined changes in 30-year averages in sea surface temperature, air pressure and wind-stress records.

Dr Scott Power and Dr Ian Smith will be presenting their findings at GREENHOUSE 2007 in Sydney. This conference will be held at the Hilton Sydney from Tuesday October 2 to Friday October 5.

Further information:
Dr Scott Power, Bureau of Meteorology, mob: 0400 650 483
Dr Ian Smith, CSIRO, phone: 03 9239 4539
Media assistance:
David Grant, Media Relations Adviser, Bureau of Meteorology, mob: 0439 452 424

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