Atmospheric blocking high-pressure systems

The “atmospheric blocking” term in meteorology describes the large-scale quasi-stationary high-pressure systems that can persist for several days or weeks, blocking and diverting the usual path of synoptic disturbances (cyclones). While cyclones can pose an immediate threat to human activities with the sudden burst of extreme rainfall and strong winds, the impact of blocking high-pressure systems is noticeable after several months. 

Since the end of 2021 and up to May 2022, blocking highs in western Europe have occurred with a high frequency, something that has led to a prolonged period of drought. The following map shows the anomaly of geopotential height values at 500 hPa, approximately 5 km above sea level. The red contours show the persistent high-pressure systems in northwest Europe and in northeast Siberia, as well as a weaker one in western Atlantic.

This is not the first time that atmospheric blocking prefers western Europe instead of the mid-Atlantic area (Azores High). What is worrisome, is the lack of climate models’ ability to simulate these high-pressure systems, and what the future holds. A study that was conducted in 2020 by scientists at CNR-ISAC and École Normale Supérieure highlighted the incompetence of climate models to correctly reproduce the atmospheric blocking in the historic period (1951-2017), but all models show a worldwide reduction of the blocking activity, especially in winter. Nevertheless, in the past 20 years the observations show an increase of blocking high activity in northwest Europe, and 2022 so far has been a great example of that.