Tuesday, 13 November 2018

Stalling summer weather patterns set stage for extreme heat

Stalling summer weather patterns set stage for extreme heat
21 Aug

Aug. 20 (UPI) — Summer weather patterns are slowing down, a new survey confirms.

As a result of summer weather stalling, a string of warm days are more likely to turn into a heat wave, and light showers are more likely to become a torrential downpour, triggering flooding.

Research suggests a slowdown of planetary waves, atmospheric waves in the upper troposphere, are behind the stalling patterns. Under normal conditions, planetary waves lend dynamism to Earth’s weather patterns — no longer.

“When they get trapped due to a subtle resonance mechanism, they slow down so the weather in a given region gets stuck,” Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research, said in a news release. “Rains can grow into floods, sunny days into heat waves and tinder-dry conditions into wildfires.”

Dozens of studies have explored the links between planetary waves and regional weather patterns. Scientists at the Potsdam Institute and elsewhere revisited many of these studies, looking for agreement among the data and analysis.

Most studies suggest Arctic warming explains the slowdown in planetary waves. Tropospheric currents are drive by temperature difference between polar air masses and those closer to the equator. But man-made climate change has caused the Arctic to warm more than the rest of the Northern Hemisphere, slowing planetary waves.

However, the latest scientific survey — published Monday in the journal Nature Communications — suggests there are other factors at work.

“There are many studies now, and they point to a number of factors that could contribute to increased airstream stalling in the mid-latitudes,” said Simon Wang, a climate researcher at Utah State University. “Besides Arctic warming, there’s also the possibility of climate change-induced shifting of the storm tracks, as well as changes in the tropical monsoons.”

Climate models suggest global warming is intensifying Indian summer monsoon rainfall. The development is likely to slow global airstreams, reinforcing stalling patterns.

Another study published earlier this year showed global warming and stalling patterns likely explained Hurricane Harvey’s record rainfall totals.

“All of these mechanisms do not work in isolation but interact,” said Wang. “There is strong evidence that winds associated with summer weather systems are weakening and this can interact with so-called amplified quasi-stationary waves. These combined effects point towards more persistent weather patterns, and hence more extreme weather.”

In a separate study, published in the journal Scientific Reports, Potsdam scientists showed the slowing of planetary wave patterns increases the probability of wildfire disasters. The data showed stalling patterns helped facilitate the wildfire that devastated Canada’s Alberta region in 2016.

“Our analysis reveals that beyond that single event, actually from the 1980s on, planetary waves were a significant factor for wildfire risks in the region,” said researcher Vladimir Petoukhov. “Since it is possible to detect the wave patterns with a relatively long lead time of 10 days, we hope that our findings can help forest managers and fire forecasters in the future.”

Scientists say more modeling work is needed to more accurately differentiate between the effects of natural variability and atmospheric patterns, but that the link between slower planetary waves and more extreme weather is strong.

“While we do not have certainty,” said PIK researcher Dim Coumou, “all in all the state of research indicates that changes in airstreams can, together with other factors, lead to a phenomenon that sounds funny but isn’t: extreme extremes.”

Source: https://www.upi.com/Stalling-summer-weather-patterns-set-stage-for-extreme-heat/6411534774638/


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