Many extreme weather events, such as heat or frost waves, are caused by a blockage of the paths followed by jet streams in the upper atmosphere, whose flows follow the same dynamics of road traffic. The discovery - made by two University of Chicago researchers, Noboru Nakamura and Clare SY Huang, and published in "Science" - will allow to simplify meteorological models and improve long-term forecasts.
Jet streams are massive high-speed airflows that move into the upper atmosphere from west to east, greatly affecting weather conditions.
When a jet stream begins to screw on itself, it prevents meteorological systems from moving to the east, a phenomenon known as an atmospheric block, creating critical situations. Big atmospheric blocks were responsible, for example, for the heat wave that hit Europe in 2003, the drought in California in 2014 and Hurricane Sandy, which devastated the Caribbean and the eastern coast of the United States in 2012.
The atmospheric blocks have been studied for decades but until now they have not been able to understand why and when they are formed, preventing the assessment of the medium to long-term risk that a certain region is affected by extreme events.
While trying to develop various models of atmospheric blocking, Nakamura and Huang realized that the equations of one of them were almost identical to those identified some decades ago by mathematicians and engineers who study urban road traffic to describe the formation of traffic jams.
"We have thus discovered that a jet stream has a capacity for 'meteorological traffic', just as a road has a certain capacity of traffic; when this is overcome, the block manifests itself as congestion, "said Huang. When more jet stream flows converge, or some of them are slowed by particular topographic features of the underlying area, such as mountains or coasts, a atmospheric "traffic jam" that causes a blockage.
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The model developed by researchers on this basis is much simpler than those now available and appears able not only to explain, but also to predict atmospheric blocks.
By applying this model to the ongoing climate change, the researchers add, it can be predicted that at global level atmospheric blocking phenomena will most likely increase, as heating approaches jet streams to the limit of their abilities, but also that there will be significant regional differences; the Pacific Ocean, for example, could even see a reduction in blockades in the coming decades.