Wednesday, 3 October 2007

MEDIA RELEASE

Reconstructing cyclone data

Bureau of Meteorology researchers are reaching into the past to recreate a complete history of tropical cyclone behaviour in the Australian region in research presented as part of the GREENHOUSE 2007 Conference in Sydney.

Bureau climatologist, Dr Blair Trewin, said commonly understood trends in cyclone behaviour may reflect problems with our existing data.

Tropical Cyclones are low pressure systems in the tropics that, in the Southern Hemisphere, have well defined clockwise wind circulations in which the wind surrounding the centre or eye of the cyclone are described as gale force or stronger (i.e. sustained winds of 63 km/h or greater with gusts in excess of 90 km/h).

"Currently there is no consistent long-term tropical cyclone data for the Australian region, particularly prior to the introduction of satellite-based observation methods since the mid 1980's," said Dr Trewin.

"Prior to satellite and radar observations some cyclones which did not make landfall — or did so on remote parts of the coast — are unlikely to have been reported."

"Also, cyclone intensity was often underestimated prior to the introduction of current satellite analysis techniques in the mid-1980s, and the full intensity of the most severe cyclones was only detected in a few cases where they passed directly over instruments".

The first part of this project is complete and has resulted in corrections in cyclone tracks, and the removal of duplicates, weak systems, and extratropical cyclones (non-tropical cyclones, such as the east coast lows that form off the New South Wales coast.)

The next phase will completely recreate the record from source data and lead to the compilation of a cyclone intensity and track data set which is much more reliable.

Number of severe and non-severe tropical cyclones in Australian region, 1969-2005.