Lightning forms during a storm due to the separation and reunion of electrical charges in the clouds, creating spectacular electrical discharges between different clouds or between a cloud and the ground.
When a storm intensifies, the tiny ice particles present in a cloud will collide and rub against each other. These frictions generate electric charges, just like when you rub a balloon on a sweater. Gradually, areas form within the cloud: generally, the upper part becomes predominantly positive, while the lower part is negative. This electrical imbalance creates a huge tension between the cloud and the ground (or sometimes between two clouds). When the accumulated charges become too strong, the air, which is normally insulating, eventually breaks down, causing a brief but powerful electric current known as a lightning bolt.
When a cloud becomes stormy, it becomes electrically charged by accumulating two types of charges: generally positive charges at the top and negative ones at the bottom. This separation of charges is due to the rapid movements of water droplets and ice crystals inside the cloud. When these particles collide, they exchange electrons and become charged. Like in a large natural battery, the amount and distribution of these accumulated charges determine the power and frequency of future lightning strikes. The more the cloud accumulates significant opposite charges, the more numerous and powerful the lightning will be. Without this accumulation of electrical charges, no lightning is possible!
In a thundercloud, the electric potential differences work somewhat like a gigantic battery. When negative charges accumulate at the base of the cloud and positive charges remain mostly at the top or on the ground, a huge electric tension builds up. This tension increases until the air itself, normally an insulator, eventually gives way. At that point, it "cracks": the air abruptly turns into a conductor, allowing electrons to rush at high speed to rebalance the charges. And it is precisely this lightning-fast rebalancing caused by these enormous potential differences that triggers the lightning. The greater this difference, the more violent the lightning will be.
At the start, an intense electric field is created between two areas of opposite charges, usually within the thundercloud or between the cloud and the Earth. Quickly, a first discharge called a downward leader originates from the cloud: this "precursor" progresses in small successive jumps, forming an electrically conductive path downward. Then, as this discharge approaches the ground, an upward discharge rises from the Earth's surface or certain objects (such as trees, poles, or buildings). As soon as these two discharges meet, a powerful connection occurs, and this is what you see as the famous main lightning strike. The intense electric discharge instantly heats the air, causing a sudden expansion: this is what produces the recognizable sound of thunder.
The size of the thunderstorm cloud plays a major role: the larger it is, the more numerous and powerful the lightning will be. The amount of moisture available in the air is also decisive: very humid air promotes intense electrical activity. A very unstable atmosphere, with strong upward currents called convective currents, also enhances the frequency and severity of lightning. Finally, the ambient temperature can influence the phenomenon: storms are often more electrical when it's hot, as heat intensifies vertical air movements. Some regions are simply more prone to lightning due to their climate and local environment, such as the proximity of bodies of water or particular terrain.
A lightning strike can produce a temperature of up to about 30,000 °C, which is nearly five times hotter than the surface of the Sun!
Every second, nearly 100 lightning strikes hit our planet, representing about 8 million lightning strikes per day worldwide.
The phenomenon known as 'positive lightning' originates from the tops of thunderstorm clouds and can be up to ten times more powerful than traditional lightning: it is often responsible for the most destructive impacts.
The natural glass known as 'fulgurite' forms when the intense heat of a lightning strike hits sand or sandy soil, instantly fusing these materials into astonishing tubular structures.
An intracloud lightning is an electrical discharge that occurs within the same cloud or between two nearby clouds, without reaching the ground. In contrast, a cloud-to-ground lightning is an electrical discharge that directly connects the cloud to the ground, representing a direct interaction with the Earth's surface.
Inside and away from windows or conductive objects, using a mobile phone is generally not dangerous. However, outdoors or in contact with conductive materials (cables connected to an electrical outlet), there may be an increased risk of lightning or electrical shocks.
Tall objects reduce the distance between the electrically charged cloud and the ground, thereby facilitating the path of electrical current with lower resistance. This explains the tendency for lightning to strike trees, tall buildings, or metal poles.
Lightning generally favors the path of least electrical resistance. Metals such as copper, steel, or aluminum provide better electrical conduction and are therefore often struck by lightning if they represent the easiest routes to the ground.
A lightning rod protects structures by providing a preferred path for lightning to reach the ground. It consists of a metal rod placed at a height, connected to the ground via a conductive cable. During a storm, it attracts lightning and directs the electrical energy straight to the ground, thereby minimizing the risk of material and human damage.
Because the speed of light is much faster than that of sound, the lightning reaches our eyes almost instantly, while the thunder takes about 3 seconds to travel 1 kilometer. The greater the interval between the flash and the sound, the farther away the storm is.
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