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Jet stream pattern and ‘heat domes’ fuel soaring temperatures around globe

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Map animation displaying the motion of the jet stream and temperature throughout the northern hemisphere from July 17 to 23

© Noaa Cartography by Steven Bernard ©FT

Map animation displaying the motion of the jet stream and temperature throughout the northern hemisphere from July 17 to 23

Simultaneous heatwaves and flooding in swaths of the US, Europe and Asia are being fuelled by a selected jet stream sample that creates a sequence of “warmth domes” which in flip drive up temperatures, scientists say.

The fast-moving band of air that could be a key driver of worldwide climate programs has been locked for weeks in a sample characterised by 5 giant U-bend shapes, dubbed “wavenumber 5”.

Scientists say such a sample was additionally behind the intense climate seen round seen the world final yr.

Warmth domes type within the areas south of the U-bends, elevating temperatures in locations inside the dome as scorching air is trapped and warms as it’s squashed downwards.

Many areas are “struggling mightily” underneath these warmth domes which were “parked in place” for a few month, stated Jennifer Francis, a scientist on the Woodwell Local weather Analysis Heart.

Scientists have been making an attempt to grasp whether or not the band of fast-moving air that controls climate within the mid-latitudes is altering in a approach that makes heatwaves and rainfall extra frequent and protracted.

Graphic explaining how a heat dome works  Warm Pacific air gets trapped in jet stream, forming ‘omega block’ loop. Warm air expands upwards. High pressure forms a dome that prevents warm air from escaping. High pressure forces warm air back to the ground. Warm air compresses as it sinks, releasing more heat. Heat causes ground to lose moisture, creating further warming and increasing likelihood of wildfires.

Following the month of June as the most popular on report globally, the World Meteorological Organisation has stated preliminary information indicated that the beginning of July was the “hottest week on report”.

Nationwide meteorological businesses stated information had been set in locations together with China’s Xinjiang, which hit 52.2C final week, and Italy’s Rome, which hit 41.8C.

Simultaneous heatwaves additionally affected elements of the US, Europe and China at an analogous time final yr, when a wavenumber 5 sample was current.

Scientists are clear that excessive climate occasions will change into extra frequent and intense as local weather change accelerates. The world has already warmed by a minimum of 1.1C in contrast with pre-industrial occasions. 

How local weather change is altering the behaviour of the jet stream is much less clear, and researchers try to untangle the connection between the 2 phenomena, and what which may imply for future climate patterns. 

“It’s solely regular for the jet stream to have this variability and get caught in sure positions,” stated Cathryn Birch, professor of meteorology and local weather on the College of Leeds within the UK. “It is not likely potential to say whether or not local weather change has influenced that.”

Though heatwaves can happen within the absence of a wavenumber 5 sample, the presence of the naturally occurring phenomenon can drive simultaneous heatwaves because it creates a sequence of warmth domes.

Warmth domes could be self-reinforcing, since dry scorching floor can warmth up sooner on account of the shortage of moisture which may in any other case evaporate and assist cool the environment. 

Human-induced local weather change exacerbates the situations, provided that common world temperatures are increased than they’d in any other case be.

At current, marine heatwaves within the Pacific and Atlantic oceans have been additionally “dumping warmth into the environment”, stated Francis.

“It’s actually outstanding what’s occurring [in the oceans] proper now and really disturbing,” she stated. “After we get wavenumber 5 as nicely it accentuates the warmth that’s being dumped into the environment.”

Scientists have warned that this yr and subsequent are prone to be unusually scorching on account of the creating El Niño climate phenomenon, which is related to a hotter Pacific Ocean floor temperature.

Nevertheless, most concur that El Niño’s penalties usually tend to be felt in coming months because the phenomenon strengthens.

Wanting forward, researchers stated the wavy jet stream sample was anticipated to proceed into August, though it might shift sample or location, which might alter which areas are affected by warmth domes and rainfall.

The wavy jet stream was in a barely totally different place in June, for instance, inflicting the UK to expertise unusually scorching temperatures and Europe to endure heavy rainfall.

Areas which can be between warmth domes — comparable to elements of the US and South Korea in July — could expertise sudden rainfall and flash flooding. 

“You want one thing fairly large to kick [a wavenumber 5 pattern] out of form,” comparable to a considerable amount of vitality from tropical thunderstorms, stated Paul Davies, chief meteorologist on the UK’s Met Workplace.

The sample is much less widespread in winter within the northern hemisphere, as there may be extra vitality within the environment created by climate comparable to storms, which permits the jet stream to plough by potential waves.

There have been indications the jet stream sample is perhaps shifting and altering additional, forming right into a wavenumber 6, which might imply a further U-bend, stated Davies.

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