Abstract
Low pressure systems off the southeast coast of Australia can generate intense rainfall and associated flooding, destructive winds, and coastal erosion, particularly during the cool season (April–September). Impacts depend on coastal proximity, strength and latitude. Therefore, it is important to investigate changes in frequency, duration, location, and intensity of these systems. First, an existing observation-based database of these low pressure systems, for 1970–2006, is extended to 2019, focusing on April–September and using archived Australian Bureau of Meteorology MSLP charts. Second, data consistency between 1970 and 2006 and 2007 and 2019 is confirmed. Third, permutation testing is performed on differences in means and variances between the two 25-year intervals 1970–1994 and 1995–2019. Additionally, trends in positions, durations and central pressures of the systems are investigated. p-values from permutation tests reveal statistically significant increases in mean low pressure system frequencies. Specifically, a greater frequency of both total days and initial development days only, occurred in the latter period. Statistically significant lower variance for both latitude and longitude in systems that developed in both subtropical easterly and mid-latitude westerly wind regimes indicate a shift south and east in the latter period. Furthermore, statistically significant differences in variance of development location of explosive low pressure systems that develop in a low level easterly wind regime indicate a shift further south and east. These changes are consistent with fewer systems projected to impact the east coast. Finally, important changes are suggested in the large scale atmospheric dynamics of the eastern Australian/Tasman Sea region.
Highlights
In recent decades, global warming (GW) has influenced numerous Australian weather and climate events, including an increased frequency and intensity of heatwaves, severe and extended droughts, and record rainfall rates and totals [1]
This finding contrasts with no change or weak declines in east coast lows (ECLs) found by Browning and Goodwin [13] and Pepler [28], but consistent with a lack of change in Explosive ECLs found in this study
The position changes of maxima for these two groupings possibly are related to changes in the large scale circulation that have influenced eastern Australian/Tasman Sea longitudes over the last 50 years and require further research
Summary
Global warming (GW) has influenced numerous Australian weather and climate events, including an increased frequency and intensity of heatwaves, severe and extended droughts, and record rainfall rates and totals [1]. An ECL is defined in this study, following [6], as a cyclone near SE Australia that can be caused by both mid-latitude and tropical influences over a range of levels in the atmosphere. It is not yet known how the GW trend in recent decades has influenced the spatial and temporal distribution of the ECLs. Most studies to date have found little change during the 20th Century and conclude that there is uncertainty concerning their future spatial and temporal distribution, as described in a recent review of Australian east coast low pressure systems [6]. Studies focused on specific climatological features of the systems [2,7], modelling studies of extreme cyclogenesis [8], or ensemble forecasting techniques [9]
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