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A warming Arctic creates weather extremes in our latitudes – ScienceDaily

Atmospheric researchers at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), have now developed a climate model that accurately maps the frequently observed whorl of the jet stream, a large airflow over the northern hemisphere. The breakthrough came when scientists combined their global climate model with a new machine learning algorithm in the field of ozone chemistry. With their new combo model, they can now show that the undulating course of the jet stream in winter and the resulting extreme weather conditions in Central Europe and North America are the direct result of climate change. Their results were published on May 28, 2019 in the Nature Online Portal Scientific Reports .

Climate researchers around the globe have been investigating for years whether the jet stream is curving across the northern hemisphere ̵

1; observed more frequently in recent years – is a product of climate change or a random phenomenon due to natural fluctuations in the climate system. The term "jet stream" refers to a powerful band of west winds over the mid-latitudes that drive the major weather systems from west to east. These winds whip around the planet at a height of approximately 10 kilometers, are driven by temperature differences between the tropics and the Arctic, and in the past have often reached top speeds of up to 500 kilometers per hour.

As observations confirm, the winds fluctuate increasingly. They rarely blow along a straight course parallel to the equator; Instead, they swim in mighty waves over the northern hemisphere. In winter, these waves generate unusual invaders of cold Arctic air into the mid-latitudes – like the extreme cold that struck the Midwestern US in late January 2019. In summer, a weakened jet stream leads to a prolonged spread of heat waves and dry conditions, such as in Europe z 2003, 2006, 2015 and 2018.

Machine learning allows the climate model to capture the role of ozone.

These basic relationships have been known for some time. Nevertheless, researchers have failed to present the fluctuating course of the jet stream in climate models realistically, or to demonstrate a link between stalling winds and global climate change. Atmospheric researchers at the AWI in Potsdam have now removed this hurdle and added an innovative component for ozone chemistry to their global climate model. "We have developed a machine learning algorithm that allows us to model the ozone layer as an interactive element in the model, reflecting the interactions between the stratosphere and the ozone layer," says lead author and AWI atmospheric researcher Erik Romanowsky. "With the new model system, we can now realistically reproduce the observed changes in the jet stream."

According to the team's results, sea ice retreats and the associated increased activity of atmospheric waves produce significant, ozone-enhanced warming of the polar stratosphere. Since the low polar temperatures form the engine of the jet stream, the rising temperatures in the stratosphere cause a hesitation. This weakening of the jet stream is now spreading down from the stratosphere and creating weather extremes.

The weakened jet stream is due to climate change

Researchers can also analyze the causes of the meandering beam in more detail. "Our study shows that the changes in the jet stream are at least partially due to the loss of Arctic sea ice, and as the ice cover continues to decrease, we believe that both the frequency and intensity of the extreme weather events previously observed in the mid-latitudes will increase "says Prof. Markus Rex, Head of Atmospheric Research at the AWI. "In addition, our findings confirm that the more prevalent winter cold spells in the US, Europe, and Asia are by no means a contradiction of global warming, but are part of anthropogenic climate change."

The efforts also represent significant technological advances: "Following the successful use of machine learning in this study, we are now using artificial intelligence in climate modeling for the first time to arrive at more realistic climate modeling systems which we believe will provide more reliable climate projections and a more robust basis for policy making, "says Markus Rex.

During the Arctic expedition MOSAiC, which will begin in September and when the German research icebreaker Polarstern will drift for a year along with the sea ice through Central Arctic. The researchers plan to collect the latest ice and atmospheric d at one. This will help them to apply the new climate model to the future in order to simulate the future evolution of the Arctic climate and sea ice. Markus Rex explains: "Our goal is to understand in detail the progress of the Arctic sea ice decline, because only then can we estimate how and to what extent the changes in the Arctic will lead to extreme weather conditions in the EU middle latitudes."

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