Interesting stuff - thank you.
Originally Posted by: polarwind
Great to see interest… the southern hemisphere weather is very different to the north. Less landmass and mountain ranges, so we don’t see the zonal disruption. So an event like this is unusual. The below is taken from an amateur meteorologist I follow from Queensland.
Earlier this July, the temperature more than 20 kilometres above the east Antarctic coastline suddenly warmed by about 50 degrees Celsius in a week — an event called a sudden stratospheric warming (SSW).
While SSWs occur every other year in the northern hemisphere, they are extremely rare in the southern hemisphere, and have never previously been observed in winter.
The rapid polar warming is now beginning to filter down towards the surface in the form of higher pressure over Antarctica, a set-up which has the potential to impact Australia's weather through August and possibly well into spring.
Typically this sudden change over the stratosphere will then filter down and disrupt the troposphere (the layer of atmosphere where weather occurs), which can result in prolonged spells of extreme weather for weeks.
Technically the warming of the stratosphere is required to average at least 25C to be classified as a true SSW, and while this event's warming has doubled that figure near the east Antarctic coast, the average warming over the whole of Antarctica may have so far peaked just below the threshold.
A pair of leading international weather models are predicting the SSW footprint will continue into August, which could mean frequent stormy conditions for the southern states, and possibly renewed bursts of gale-force winds and heavy alpine snow in the weeks ahead.
While the weather is already being impacted by the warm stratosphere over Antarctica, its ongoing presence could instigate a chain of events with the potential for long-lasting impacts on southern hemisphere atmospheric conditions.
A critical step in this prolonged influence would be a reduction in this year's ozone hole. Essentially the more ozone the more heating occurs and the weaker the polar vortex, while a depleted ozone layer, like we saw in 2023, leads to a colder and stronger polar vortex.
The above process would lead to a similar expansion of westerly winds through spring, bringing further above-average rain to the southern coast and ranges, while again leading to warmer and drier conditions for the east coast.
There is no guarantee a second anomalous weather system near Antarctica won't reverse the stratospheric warming through the coming weeks. Another wildcard is the residual moisture from the Hunga-Tonga volcano, which could counterbalance the excess ozone.
So in summary in simple terms more winter systems for the southern states are likely for the remainder of July and throughout August. Current modelling suggests a drier remainder of winter for Queensland possibly extending into September. Enhanced fire risk from late August for the eastern half of Queensland. With a meridional jet stream pattern likely highly variable conditions with sharper wind changes alternating from warmer ahead to cooler behind with an enhanced risk of severe thunderstorms as the temperatures warm late August into September. The risk of spring frosts are higher also particularly southern Queensland regions.