Extreme weather in Europe is caused by the displacement of high-altitude jet streams

Abnormal heat, droughts, floods and other extreme weather events in Europe are directly related to deviations from the “routes” of high-altitude jet streams in the troposphere over the North Atlantic, climatologists found. In particular, the deflection of the jets to the north leads to droughts in northwestern Europe, and a deviation to the south – to fires in south-eastern Europe. Especially this effect has become noticeable since the 60s of the XX century, when the frequency of such events has greatly increased, scientists write in an article published in Nature Communications.

High-altitude jet streams – winds with high velocities (more than 25 meters per second) – are observed in the upper layers of the troposphere, at altitudes from 5 to 16 kilometers. They affect the formation of weather and climate on a global scale. In particular, El Niño, the active phase of temperature and direction changes in the water currents in the Pacific, leads to the displacement of high-altitude jet streams, which in turn affects the distribution of tropical cyclones. And if the Pacific jet streams exert a greater influence on the American climate, the weather in Europe is more sensitive to a change in the direction of high-altitude flows in the polar region.

To study the possible relationship between climatic changes in Europe and the direction of the North Atlantic jet stream, a group of climatologists from the USA and Switzerland, led by Valerie Trouet of the University of Arizona, compared the anomalies of this stream with historical records of extreme weather events in Europe. To estimate the deviations of atmospheric fluxes, scientists used data obtained from annual rings on trees in the British Isles and in the northeastern Mediterranean.

As a result, climatologists managed to restore information about the approximate direction and strength of the high-altitude jet stream every August, beginning in 1725. In some cases, the accuracy of this method was rather low, but in this way it was possible to obtain a qualitative picture in almost 300 years, during which no climatic observations were made. To obtain information on jet streams from 1978 to the present, scientists used data from modern meteorological measurements. The authors note that the maximum speed for the North Atlantic high-altitude jet stream in winter, but even for summer weather, it has a rather strong effect.

Scientists have shown that the correlation between the anomalies of atmospheric flows and extreme weather in Europe does exist. In particular, the deviation of the north-Atlantic jet stream to the north leads to droughts and anomalous heat in northwestern Europe, with rain and floods increasing in southeastern Europe during this period. At the same time, the shift of flows in the south direction, on the contrary, causes fires in south-eastern Europe and floods in the British Isles.

In addition, climatologists have found that since the 60s of the XX century, the frequency and amplitude of the oscillations of the direction of the polar jet stream have sharply increased. This has become one of the mechanisms to more and more often reach record temperatures in the summer, an increase in the number of fires and other manifestations of extremely hot weather.

Scientists note that polar jet streams (in particular the North Pacific stream), which combine into a single system with a North Atlantic stream, lead to a change in weather in North America. For example, their bias led to an increase in cold weather in the northern part of the continent and droughts in California.

If high-altitude jet streams in the Earth’s atmosphere can interfere with air travel and have a negative impact on the climate, then high-speed flows in the atmospheres of other celestial bodies have their shortcomings from the human point of view. In particular, jet streams on exoplanets conceal biomarkers from telescopes and prevent scientists from determining the presence of life on them.