Our study shows that the specific locations and timing of the 2018 summer extremes weren't random but directly connected to the emergence of a re-occurring pattern in the jet stream that stretches around the entire Northern Hemisphere.

Kai Kornhuber, lead author of the study

• The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously
• Shows that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern
• Shows that this pattern constitutes an important teleconnection in Northern Hemisphere summer associated with prolonged and above-normal temperatures in North America, Western Europe and the Caspian Sea region
• Finds that this pattern was also observed during the European heatwaves of 2003, 2006 and 2015 among others
• Shows that the occurrence of this wave 7 pattern has increased over recent decades