Summary

Australian hot and dry extremes induced by weakenings of the stratospheric polar vortex

Extreme hot and dry conditions have large impacts on agriculture. Recently, scientists have found that changes in the Antarctic polar vortex can provide early warning of these conditions in sub-tropical and eastern Australia. The Antarctic polar vortex (APV) is a strong wind pattern in the stratosphere that typically circles the earth at the latitude of the Antarctic coast. Analysis of 40 years of data show that a weak APV in spring, greatly increases the odds of hot and dry conditions across spring and early summer. Nine years showing a weak spring APV were compared to 29 years of a normal or strong spring APV. The chance of the following October to January being in the top 20% for maximum temperature and the bottom 20% for rainfall was 4 to 8 times greater in the years with the weak APV for large portions of Queensland and northern New South Wales. In the Maranoa and western portion of the Western Downs regions of southeast Queensland, all occurrences of the maximum temperature in the top 20% were in with years of a weakened APV. In these years, maximum temperatures were 1 to 2 °C hotter and conditions were drier across most of New South Wales, southern and central Queensland, and parts of eastern South Australia. This indicator could provide as much as a season’s notice, enabling more lead time for farmers to prepare for these conditions.