Atmospheric researchers at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now developed a climate model that can accurately depict the frequently observed winding course of the jet stream, a major air current over the Northern Hemisphere.
Atmospheric researchers at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now developed a climate model that can accurately depict the frequently observed winding course of the jet stream, a major air current over the Northern Hemisphere. The breakthrough came when the scientists combined their global climate model with a new machine learning algorithm on ozone chemistry. Using their new combo-model, they can now show that the jet stream’s wavelike course in winter and subsequent extreme weather conditions cold air outbreaks in Central Europe and North America are the direct result of climate change. Their findings were released in the Nature online portal Scientific Reportson 28 May 2019.
For years, climate researchers around the globe have been investigating the question as to whether the jet stream’s winding course over the Northern Hemisphere – observed with increasing frequency in recent years – is a product of climate change, or a random phenomenon that can be traced back to natural variations in the climate system. The term “jet stream” refers to a powerful band of westerly winds over the middle latitudes, which push major weather systems from west to east. These winds whip around the planet at an altitude of roughly 10 kilometres, are driven by temperature differences between the tropics and the Arctic, and in the past, often reached top speeds of up to 500 kilometres per hour.
But these days, as observations confirm, the winds are increasingly faltering. They less often blow along a straight course parallel to the Equator; instead, they sweep across the Northern Hemisphere in massive waves. In turn, during the winter these waves produce unusual intrusions of cold air from the Arctic into the middle latitudes – like the extreme cold that struck the Midwest of the USA in late January 2019. In the summer, a weakened jet stream leads to prolonged heat waves and dry conditions, like those experienced in Europe in e.g. 2003, 2006, 2015 and 2018.
Image: The changes in the jet stream are at least partially caused by the decline in the Arctic sea ice, according to the results of the investigations. (Photo Credit: Marcel Nicolaus)