How is the jet stream connected to the simultaneous heat waves of the entire globe?

The deadly heat waves that raged in Europe, the United States, and China this month and caused transportation disruptions have one thing in common: a unique form of jet stream called “wavenumber 5.”

Scientists are competing to understand whether the fast-moving air bands that control mid-latitude weather are changing in ways that make heat waves more frequent and persistent.

Paul Williams, a professor of atmospheric science at the University of Reading in the United Kingdom, said: “Jet streams are the main driving force for our weather. Jet streams are like conveyor belts, causing storms one after another.”

It also resembles the shape of the Greek letter omega, so it can also generate heat waves when it is formed into a U-shape called an “omega block”.

Currently, a global pattern of five large waves orbits the world, with simultaneous heat waves across the continent. This pattern, known as wavenumber 5, can last for weeks and causes the hot regions to remain hot for extended periods of time.

More than 900 million people have experienced heat waves in China, and more than 70 meteorological stations broke records this month. In the United States, Texas and Oklahoma have record highs every day, with more than 20 states issuing heat warnings.

Britain hit a record high of 104.5 degrees Fahrenheit this week, but France and Spain set record temperatures in the fight against wildfires after weeks of extreme heat waves.

Stephen Belcher, Chief Scientist of the Met Office, said: “Met Office forecasters are scrutinizing this wavenumber 5 pattern very closely to see how long it lasts,” he added.

Belcher said three factors contributed to the heat wave in Europe. Wave number 5 pattern of jet stream. The rise in the average temperature of the world. And especially the dry soils around the Mediterranean are the result of prolonged heat.

Dim Coumou, a climate scientist at VU Amsterdam, has two important patterns in summer jet streams. He said there are 5 or 7 waves and they tend to stay in the same place when they are formed. “If such a wave pattern is stagnant and lasts for a long time, we usually see heat waves at the same time,” he said.

More and more research is trying to answer the question of how exactly jet streams are changing due to global warming and what this means for future weather patterns. Due to human activities, the temperature has already risen by about 2 degrees Fahrenheit even before the Industrial Revolution.

The jet stream itself changes its behavior in the long run and appears to slow down in the summer. This increases the likelihood of an “omega block” pattern.

Jennifer Francis, an atmospheric scientist at the Woodwell Climate Research Center in Falmouth, Massachusetts, said the rapid warming of the Arctic Circle seems to be responsible for this slowdown.

“In the summer, the winds are generally reduced,” Francis said. “The reason for the jet stream is that it’s cold in the north and warm in the south, due to the temperature difference. [the condition for the jet stream]”She said.

The temperature difference between these air masses is now small because the Arctic is warming much faster than the rest of the globe.

Some of the jet stream behavior has not yet been explained. “Across the Atlantic, the jet moved south in the summer,” said author Tim Woolings. Jet stream Professor of Atmospheric Physics in Oxford. “I expected it to shift north in response to climate change.”

Woolings said the recent heat wave that Britain experienced was “a little tasting” of what other parts of Europe experienced. “The real thing is happening in Spain and France,” he said.

The UK experienced two very high temperatures on July 18th and 19th, before the weather cooled. Temperatures have risen over the weeks in Spain and France.

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Climate models show that heat waves get hotter as the world’s average temperature rises. However, it can take years for researchers to know exactly how global warming affects these patterns of jet streams.

“We need a very long observation record,” Williams said. “It can take decades, or even a century, to detect changes satisfactorily.”

This story originally appeared in the July 21, 2022 edition of the Financial Times.

Copyright The Financial Times Limited 2022

Reprinted with permission.

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