Two cloud-to-ground flashes less than two seconds apart
Late summer thunderstorm, vallon de la Brague
A thunderstorm is an atmospheric phenomenon, characterized by a series of lightning and thunderbolts, which forms from a specific cloud, the cumulonimbus.
A lightning bolt can fire inside the cloud, between two clouds, between the cloud and an aircraft or between a cloud and the ground, in the latter case called cloud-to-ground lightning.
Since 1989, the Sud / Provence Alpes Côte d'Azur region has been the most blasted region of France with 1.75 cloud-to-ground lightning per km² and per year.
Over ten years (between 2010 and 2019), the Alpes-Maritimes was the department most affected by lightning in mainland France (Var being the third, immediately followed by the Alpes de Hautes-Provence).
In the case of a cloud-to-ground lightning, a first discharge is initially formed from the ground to the cloud then causing an electric arc descending from the cloud to the ground (the lightning) followed by a thunderclap:
Electric discharge of 100 million volts and more than 100,000 amps at a temperature of 30,000 degrees
Lightning length of up to 20 km over a diameter of around 3 cm
Flash duration from a few tenths of a second to about one second
When lightning occurs, it heats the surrounding air which expands at a supersonnic speed creating a sudden noise: the thunderclap. This sound wave travels at the speed of sound and arrives at an observer after the flash of lightning, which propagates at the speed of light.
