Heat and drought: are the anticyclones shifting towards the poles?

Since the beginning of 2022, the observation has been clear: the rain deficit reached -41% in January, -38% in February, -38% in March and -25% in April. The conditions in May follow the same scenario, with long hot and sunny periods. The average cumulative rainfall across the country is also the lowest in 11 years.

The fault of repetitive and lasting anticyclonic situations in France. While many appreciate this pleasant, calm and bright weather, it is responsible for a extreme drought over three quarters of Europe. These weather blocks, as the meteorologists, seem to be more and more frequent. Has the Azores High decided to change its place of residence and settle permanently in our country?

According to meteorologist Guillaume Séchet, in his study published on Weather-Cities“ since autumn 2021, the recurrence of anticyclonic blockages over Western Europe has reached remarkable levels”over the last eight months, from October 2021 to April 2022, we note “ a anomaly tall pressures all over western Europe, particularly the British Isles, northern France and the North Sea. Such anomalies smoothed over a period of eight months are major and reflect an abnormal position of the anticyclone, to the detriment of the ocean flow..

Disrupted atmospheric circulation?

The atmospheric circulation on Earth comprises several cells positioned at different latitudes. The Hadley cell lies between the equator and 30 degrees north and south latitude, where we find winds blowing from the northeast in thenorthern hemisphere and from the south-east in the south one (the trade winds). Has the atmospheric circulation really been upset in recent years due to the global warming ?

Météo France is studying the question and admits that it ” This is a topic still in the research stage, with just hypotheses”. the IPCC report, released in August 2021, specifies that, since 1980, it would seem indeed, but without certainty, that the circulation of the Hadley cell has widened, in particular towards the Northern hemisphere. According to the climate expert Meteorology Modeling for Météo France, difficult to draw conclusions on the other hand on the last months and on the last years: “ For the years 2015 to 2019, we do not really see any obvious shift in the anticyclones subtropics in relation to their climatological positions”.

Climate change almost certain in the future

Regarding future projections, the modification of the circulation atmosphericand therefore of the positioning of the anticyclones, is however very probable: “ the models of climate all agree on the fact that the cells of Hadley will have a greater meridian extension in the future, in connection with anticyclones which shift towards the poles, just like the rail of the depressions”, according to Meteo France.

Concretely, in the future, Météo France specifies that this modification should have the following consequences:

• in winter, a decrease in episodes of blockages, linked to a jet stream narrower and more intense over Western Europe;
• in summer, an increase in anticyclonic blockages, for less obvious reasons.

Europe is an exception because summer blockages tend to decrease in other regions of the world.