- Ciari, Inès, Dennis… The French coasts have suffered a multitude of storms in recent days.
- What is the reason for this phenomenon which often spares France?
- For Claude Fons, engineer specialized in marine weather, the displacement of the Azores high is at the origin of these successive waves of storms.
Ciaria, Inès, Dennis… Storms have been raging on the French coasts in recent days. What is the cause of such a succession of natural disasters and why is the wind so strong in the north of the country?
For Claude Fons, an engineer specializing in marine weather, the phenomenon is nothing new or unusual, he simply changed his destination this year.
How to explain this succession of storms which affects France these last days?
It is simply the warm air coming from the Sahara which meets the colder air from the Atlantic. When there is a collision between two airs of different heat, there is a disturbance, it is a completely normal phenomenon. When it is a large mass of heat which meets a large mass of cold air, it creates a single large storm, but when the hot air arrives in waves, there is a succession of disturbances, that we say "by train", and which arrives by wagon spaced 24-36 hours. This difference in heat is more accentuated in winter, the Atlantic being colder, which explains why there are more storms at this time.
Should we see in this phenomenon a consequence of global warming?
This kind of phenomenon has always existed. Since 1940, there have been around ten episodes of succession of storms that have struck France. In 1984, a similar phenomenon lasted from November 25 to February 23. It should not be seen as the work of global warming.
However, it is quite rare that this kind of phenomenon affects France. What has happened this year?
The Azores high is a natural barrier that normally protects against these phenomena. You have to imagine an air barrier that would be a kind of English crossroads, rejecting the disturbances far north of Europe. These successions of storms are not unusual at this time of the year, it is simply that they usually affect more Scotland, Scandinavia or Iceland. However, for two years, this anticyclone has been deported to the south, without anyone knowing for the moment why. What we do know, however, are the consequences of this displacement. The disturbances are shifted less to the north and therefore affects more Europe in the south, the British Isles and France. In summary, it is not storms that are more frequent, simply their place of impact that has changed.
It is in particular this displacement of the anticyclone which explained the wave of heat wave which Europe knew this summer, the hot air of the Sahara being no longer pushed back far and surging on the continent.
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