Significant decline in storminess over southeast Australia since the late 19th century

Abstract

Geostrophic wind speeds (geo-winds) were estimated for southeast Australia by constructing eight station triangles from instrumental records of qualitycontrolled sub-daily mean sea-level pressure from 1885 to 2008. Seasonal 95th and 99th percentiles of the geo-winds were calculated and used to identify periods of enhanced ‘storminess’ over each triangle. While the results were marked by strong multi-decadal variations, they indicated a statistically significant decline in storminess across most regions in southeast Australia since the end of the 19th century, particularly in autumn and winter. The results for winter for most regions were also statistically significantly correlated with year-to-year variations in southeast Australian rainfall although the correlation coefficients were small. Regionally averaged results showed a peak in storminess in the 1920s with least activity in the 1960s in all seasons. Although there has generally been an upturn in storminess in recent decades compared to the immediately preceding decades, it has not been of nearly the same magnitude as in the late 19th and early 20th century. While similar studies have been performed in the northern hemisphere over this length of period, we believe that this is the first time that the method has been applied to Australia. The results indicate that in addition to other climatic processes, the long-term decline in storminess may be contributing to the persistent drought conditions that are being experienced in this densely populated region