An arcus was observed in the sky of Biarritz, this Wednesday, October 9, during the passage of storm Kirk over France. But how does this spectacular phenomenon form?
The inhabitants of Biarritz witnessed a surprising phenomenon. This Wednesday, October 9, as Storm Kirk swept through the south of France before continuing its progression across France, many residents were able to observe an arcus in the sky.
This visually impressive phenomenon is a low cloud resembling a roller or dam and which only appears during a thunderstorm.
Rather dark and of imposing dimensions, this cloud forms at the front of the lower part of the cumulonimbus clouds where the majority of electrical activity and precipitation are concentrated.
Accompanying the storm, this cloud causes a current of cold air towards the ground, while the warm air located lower down climbs in altitude thanks to it, attracted by the cooler currents. The extent of the arcus is then determined by the violence of the storm.
