The winter jet stream over the Atlantic and Europe has become stronger and shifted further north on average, according to research published in Nature Geoscience by Brönnimann, Brugnara, and Kallabis. This shift correlates with a higher prevalence of southwesterly winds during winter months and a decrease in days where the jet stream is “exceptionally weak.”
Historical Air Pressure Data Reveals Jet Stream Shifts
Researchers from the University of Bern reconstructed nearly three centuries of atmospheric behavior by analyzing daily air pressure measurements. Because satellites and modern weather analyses only cover a small fraction of history, the team used records from London, Berlin, Padua, and Uppsala dating back to 1725.
By comparing these ground-level measurements, the team derived three specific metrics: the strength of the flow, its north-south position, and the angle at which it crosses Europe. These indicators allow meteorologists to understand how the jet stream—a high-altitude band of strong wind—directs high- and low-pressure systems across the continent.
Did you know? The jet stream acts as the “engine” of European weather. Its position determines whether the region receives mild air from the ocean or cold air from the north and east.
Winter Winds and the Decline of Weak Flow
The reconstruction shows the winter jet stream has increased in strength by 0.13 standard deviations compared to the pre-industrial period. While the average increase is modest, the distribution of strength has shifted. Days characterized by an “exceptionally weak” flow are now rarer than they were in the past.
This shift explains why southwesterly winds often seem dominant in modern winters. However, the researchers emphasize that winters are not becoming identical. The jet stream continues to fluctuate in strength, direction, and position, and these variations still drive significant weather events.
Comparing Historical Trends and Future Models
There is a distinction between observed historical data and future climate projections. While historical records confirm a decrease in exceptionally weak flow, climate models predict a broader reduction of extreme values across all jet stream metrics later this century. Brönnimann and colleagues note that these model predictions remain forecasts rather than proven historical trends.
Impact on European Extreme Weather
The University of Bern study established a clear link between jet stream states and various forms of extreme weather, including heavy precipitation, storms, and severe cold or snow. The researchers suggest that a reduction in extreme jet stream positions could potentially lower the risk of certain types of weather extremes.
This does not mean that storms or heatwaves will occur less frequently in general. Other climate variables continue to influence the frequency and intensity of extreme weather, and the exact relationship between the evolving jet stream and future weather extremes remains unclear.
Expert Insight: A stronger jet stream does not necessarily mean it is “straighter.” The research measured the tilt and angle of the flow, but not whether the stream makes fewer loops or meanders.
Jet Stream Dynamics FAQ
Does a stronger jet stream mean fewer winter storms?
Not necessarily. While the study shows a link between jet stream positions and extremes, other climate factors influence storms, and the overall impact on storm frequency is not yet fully clear.
How did researchers study the jet stream from 1725?
They used daily air pressure measurements from four European cities (London, Berlin, Padua, and Uppsala) to reconstruct the high-altitude flow patterns.
Why are southwesterly winds more common now?
The jet stream has shifted further north and strengthened on average during the winter half-year, which alters the path of air masses reaching Europe.