Tropical Cyclone Trends In Australia
By Paul Homewood Hurricanes have been a topic of attention recently for obvious reasons. I have done a lot of analysis of Atlantic storms, but elsewhere there is much less historical data, due to the lack of monitoring at the time. Until recently, many, probably the vast majority of, tropical cyclones blew around in the middle of the vast Pacific with little or no attention at all. Where they did affect land, there was rarely any proper equipment around to properly measure them. The Australian BOM has put together a history of TCs in their region, beginning in 1970, when satellite coverage began: Tropical cyclones in the Australian region are influenced by a number of factors, and in particular variations in the El Niño – Southern Oscillation. In general, more tropical cyclones cross the coast during La Niña years, and fewer during El Niño years. Analysis of historical tropical cyclone data has limitations due to a number of changes in observing practices and technology that have occurred over time. With new and improved meteorological satellites our ability to detect tropical cyclones has improved, as has our ability to differentiate tropical cyclones from other tropical weather systems such as monsoon depressions, which in the past may have been incorrectly named as tropical cyclones. A particularly important change occurred in the late 1970s when regular satellite images became first available from geostationary satellites above the Earth’s equator. The time series of analysed tropical cyclone activity in the Australian region (south of the equator; 90-160°E) show that the total number of cyclones appears to have decreased. However, there was a change to the definition for tropical cyclones in 1978 which led to some systems which would previously have been classified as tropical cyclones instead being considered sub-tropical systems. This contributes somewhat to the apparent decline in total numbers. The number of severe tropical cyclones (minimum central pressure less than 970 hPa) is dominated by variability with periods of lower and higher frequencies of occurrence. There is less confidence in the earlier intensity data with continuous satellite coverage commencing in 1979. http://www.bom.gov.au/cyclone/climatology/trends.shtml Accepting what they say about the pre-1979 figures, there is certainly no increasing trend, either for total or severe cyclones.
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