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How stuck air pressure systems cause heatwaves and floods

How stuck air pressure systems cause heatwaves and floods

how stuck air pressure systems drive floods and heatwaves

Climate change – fuelled by increasing greenhouse gases – is causing more Extreme weatherEvents worldwide

Many of these events, such as the “rain bomb” inundating Australia’s east coast and the Recent heatwave in Western Australia, are associated with “stalled” weather systems.

Normally, Australia’s weather systems are driven from west to east by jet streams: narrow bands of fast-flowing air high up in the troposphere, the lowest layer of Earth’s atmosphere.

But when weather systems stall in a particular place, usually because of “Blocking” high-pressure systems that stop them moving on, they can produce devastating extended periods of heat, cold or rain. These stalled weather systems will become more important as the climate changes. Expectations to grow.

Weather systems that are unstable

Blocking systemsare persistent high pressure systems that combine one or two low-pressure units with them.

High-pressure system (where the air pressure is high) are associated clear and dry weather. Low-pressure system are associated rising air, cloudiness, and rain

As the westerly jet stream is stronger, blocking tends to be less persistent at the southern hemisphere than in the northern.

Blocking highsThey are most often associated with the region of low pressure to its north. Together, the two systems work against each other to effectively “stall” the weather.

A blocking high pressure system was responsible for the deadly Russian heatwave in 2010.
Yuri Kochetov / EPA

Depending on the location, blocking systems can cause heatwaves or cold spells, floods, and dry spells. They are often associated with record-breaking weather events and human deaths – for example, the deadly heatwaves in France in 2003And Russia in 2010.

In 2021, persistent blocking system were responsible for the North America cold wavesFebruary and the record-breaking Western North America heatwaveIn June and July. The latter caused some of most severe heat events in the region, including some of the highest temperatures recorded. Canada at 49.6℃.

Slower jet streams

The slowing down or meandering of jet streams is often associated with blocking events in northern hemisphere. This occurs when the polar vortex – a large region of low pressure and cold air around the pole – breaks down.

While the exact mechanisms driving the slowing of mid-latitude jet streams is debated, the consensus attributes it to “Arctic amplification”.

The Arctic region is currently experiencing a warming rate two to three-fold faster than the rest. This difference in atmospheric warming between the Arctic region and the tropics leads to a weaker. Atmospheric pressure gradientThis slows down the jet stream.

Stalled weather in Australia

Blocking highs in Australian regionThese events are most common in the Great Australian Bight, and the Tasman Sea. These strong high-pressure system often form. SoutherlyIt is more common than usual.

These highs can stay almost stationary for a prolonged period, preventing the normal easterly progression in weather systems across southern Australia. They can occur at any season and can stay in the Australian region for several weeks or days.

A blockage high in the Tasman Ocean caused record heatwaves for Australia in 2019.
Bureau of Meteorology

Long-term blocking highMany inland Australian towns experienced record heatwaves in the south Tasman Sea between January and February 2019. Adelaide recorded the hottest day for any Australian capital city (46.6℃) on January 24.

The same blocking high prevented the movement of a deep monsoon low in North Queensland, resulting in the equivalent of a year’s rain in a week over the Townsville areaIn February 2019, early.

The rain bomb

A stalled weather system was responsible for a delay in the weather system, which occurred in February 2022. Heavy rains and floodingLarge parts of Southeast Queensland, Northern NSW were affected. It was stopped by a stubborn blockade near New Zealand that prevented it from moving to the east.

A region of low atmospheric pressure in the upper atmosphere was cut off by the westerly air current further to the south, creating a trough for low pressure at the surface. This created the perfect mix of upper and surface atmospheric conditions for what has been called a “rain bomb” or a “River in the sky”.




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The rain bomb was a major cause of flooding. Major flooding.

Brisbane, the country’s third-largest city, smashed its three-day record with 677mm of rain. Over four days, the city recorded 741mm – almost three-quarters of its annual average rainfall!

The city was subject to flooding similar in nature to the Floods in 2011 were devastating. The current floods are expected to have affected more than 15,000 homes in Brisbane.




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The Brisbane River reached its peak at 3.85m, which is below the 4.46m recorded in 2011. The however, the Two flood events are very distinctSome suburbs were more affected by flooding than 2011 in 2011,

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GympieLocated north of Brisbane, and LismoreThe flooding of the central business districts in northern NSW resulted in catastrophic flooding. Gympie was hit hard by its worst flood in 120-years, while Lismore suffered the worst flood ever recorded. This flood level surpassed the previous record by approximately 2 metres.

Lismore’s February 2022 flood smashed the previous record.
Bureau of Meteorology

Future events

Recent researchExtremely high rainfall has been observed in the past, and flooding events will increase as the atmosphere and oceans heat up under climate change.

What does this mean? Are we likely to see more rain bombs? Can we expect more rainfall and flood records worldwide?

Answer to all of these questions is yes. It’s the rising greenhouse gases, warming of the atmosphere, and warming oceans that are to blame.

The rise in global average temperatures has driven Extreme rainfall eventsSince the 1950s. Areas in Australia have warmed about 1.4℃ since 1910.




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A warmer environment can help Hold more water. For every 1℃ of extra warming, about 7% more water can be saved as water vapour. If the right atmospheric triggers are met, huge amounts of water can be released as heavy rain over unsuspecting human populations.

The jury is still out on the effects of global warming upon high-pressure blocking systems.

Currently, climate modelsYou should underestimateBoth the frequency and the duration of these blocking events can be controlled. This problem is still being studied by scientists in their models. It forms the basis for ongoing research.

However, One studyClimate change will increase the likelihood of this happening. SizeThe northern hemisphere’s high-pressure weather system has been stalled by as much 17% in this century.

An extensive high-pressure system can cause heat and cold waves to larger areas, affecting more people.

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