What is a lightning strike ?

A lightning strike is an electrical discharge generated by an electrified cloud (usually cumulonimbus) between itself and the ground (approximately 10% of cases only), inside the cloud (intra-cloud flash) or between adjacent clouds (inter-cloud flash).

Where does the roll of thunder come from ?

The noise we all associate with a thunderstorm is caused by a rise in the electrodynamic pressure estimated at 2 or 3 atmospheres. The excess pressure drops when the flash is over, producing an acoustic shock wave. The duration and the acoustic intensity of the roll will depend on the form, length, intensity and brevity of the lightning strike.

How many times is the Earth struck by lightning over a 12-month period ?

On average, there are several hundred flashes every second.

What is meant by the "keraunic level" ?

The number of days per year when thunder was heard – not to be confused with "lightning density" which equals the number of strikes / year / km2.

How do we calculate how far away a storm is ?

Divide the time in seconds between the flash and the roll of thunder by three: this gives the distance in kilometers.

Why can’t we collect the energy produced by thunderstorms ?

Although local storm intensity can be very high, the overall power released by thunderstorms over France in a given year is relatively low (100 megawatts).

Is there just one lightning flash ?

Invisible to the human eye, a lightning flash is made up of up to ten successive arcs (return strokes).

What is a fulgurite ?

Also known as "lightning stones", fulgurites are solid lumps of matter formed by the vitrification of siliceous earth, especially sandy ground, under the intense heat produced by the lightning currents in the immediate vicinity of the point of impact.

What is meant by the "buzzing bee sound" ?

More scientifically referred to as the corona effect, this is a phenomenon witnessed just prior to a thunderstorm, whereby the tips of any prominent or metallic objects can give off a characteristic buzzing sound due to the rise in the surrounding electric fields causing small electrical discharges or sparks.

How were storms explained before Franklin’s discoveries ?

In the 17th century, for example, it was thought that the phenomenon was caused when heavier clouds descended on the lighter clouds lying beneath them, compressing the air between the two cloud layers and producing a sudden release of heat, resulting in the flash and the roll of thunder.

Is there such a thing as a ‘ball lightning’ ?

Yes, the phenomenon of ball lightning is well known and has been witnessed on many occasions. Scientists are very interested in this ‘globular lightning’, but no totally convincing theory or model has ever been put forward (particularly regarding its duration of several seconds).