Australian Hot and Dry Extremes Induced by Weakenings of the Stratospheric Polar Vortex
Sudden stratospheric warmings in the Southern Hemisphere are rare compared to their regular occurrence in the Northern Hemisphere. Despite this, we show that stratospheric weakenings i.e. reductions in the strength of the upper stratospheric jet in the Southern Hemisphere can impact surface climate as well as the likelihood of extreme conditions developing over Australia from spring to summer. Our results indicate that an anomalous weakening of the Antarctic stratospheric polar vortex significantly increases the chance of occurrence of (monthly-mean) heat and dry extremes and associated fire danger by more than 4 times for large portions of subtropical eastern Australia through early summer.
Since variations in the stratospheric vortex are known to affect surface climate with a time lag of months to a season, this new connection implies that Australian hot and dry extremes can be predictable at lead times of a few months. The occurrence of extreme hot and dry conditions in Australia can have devastating effects on human health and resources, particularly during the warm seasons.
This study is the first of its kind to identify and quantify a direct link between Antarctic stratospheric polar vortex variations in spring and Australian hot and dry extremes in summer. Improving our understanding of what drives these extreme climate events will enhance our ability to predict and prepare for them with sufficient lead time.