http://www.bom.gov.au/climate/current/statements/scs72.pdf
Australia's climate was impacted by a positive Indian Ocean Dipole (IOD) in 2019, exerting a drying influence over many parts of the country. The positive IOD is characterised by cooler waters to the northwest of Australia and warmer waters further west towards Africa. Positive IOD events lead to reduced rainfall and low humidity across Australia. Recent months have seen notably low humidity, which enhances potential evaporation and increases fire danger. During October and November 2019, a prolonged negative phase of the Southern Annular Mode (SAM) enhanced the warm and dry conditions in areas of eastern Australia. Sudden Stratospheric Warming (SSW) during September above Antarctica preceded the period of negative SAM. The SSW was caused by a weakening of the stratospheric vortex (high level winds) and such events in the upper atmosphere can later affect Australia’s weather. SSW events weaken the westerly winds over the Southern Ocean, shifting the winds further north, which is what occurred in October and November 2019. For Australia, SSW events tend to have their biggest impacts in New South Wales and southern Queensland, increasing spring temperatures and decreasing rainfall.
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