Wednesday, 10 November 2004

MEDIA RELEASE - HEAD OFFICE

What happened to south-west WA's rainbearing fronts?

An Australian Bureau of Meteorology researcher has used computer analytical techniques new to climate science to describe the decline in south-west Western Australian rainfall over the past half century.

Pandora Hope applied a classification algorithm known as an artificial neural network algorithm (initially described by Professor Teuvo Kohonen in the early 1980s and applied to fields as diverse as robotics and linguistics) in a hindsight study of synoptic situations - the familiar 'weather maps'. Results to date show a decrease of 17 per cent in synoptic situations linked with wet conditions (troughs), and an 8 per cent increase in 'dry' synoptic situations (high pressure ridges) (diagram).

Ms Hope's work is part of the Indian Ocean Climate Initiative focussed on understanding the causes of declining regional rainfall in south-west WA.

"The causes of the serious winter rainfall decline are not thoroughly understood," she says. "Is it a decrease in troughs, more high pressure systems, different synoptic systems, less rain from systems ... or a combination? Model analysis of rainfall does not give enough insight - we must look at the pressure maps."

Ms Hope defined more than 20 synoptic situations, and analysed twice-daily pressure maps in June and July between 1958 and 2003. She will now extend the study to incorporate charts of weather patterns under Greenhouse scenarios, to identify possible future changes.

Abstract: www.bom.gov.au/announcements/media_releases/ho/20041110ph.pdf

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