Lightning is an electrical discharge caused by an imbalance between the storm clouds and the ground, or within the clouds themselves. Most lightning strikes occur within clouds.
Three elements are needed to cause lightning:
- a strong atmospheric instability, caused by a vertical temperature difference with hot air below and cold air above;
- a trigger, which generates movement in the air. This factor can be the radiant heat of the sun or a mountain range.
During a storm, the rain, ice or snow particles that collide inside the clouds increase the imbalance between them and the ground and negatively charge their lower sections. The objects on the ground, such as bell towers, trees and the Earth itself, charge positively, creating an imbalance that nature tries to fix by passing current between the two charges. The discharged electricity is so strong that the lightning channel can reach 20,000-30,000°C. In fact, it can heat the surrounding air to a temperature five times warmer than the sun’s surface. This heat causes the air to expand and vibrate quickly, creating the thunder that we hear shortly after seeing a flash. Thunder can help us understand how distant the lightning has fallen: since the sound travels about 1 kilometer every 3 seconds, it is sufficient to divide by 3 the number of seconds between lightning and thunder.
Lightning strikes that reach the ground (cloud-to-ground, in the image) are a common phenomenon – about 100 hit the earth’s surface every second – yet their power is extraordinary. Each flash can hold up to a billion volts of electricity. Lightning strikes of this type begin when a series of negative charges, starting from the bottom of a thundercloud, form a segmented path directed towards the ground at a speed of about 200,000 mph. Each of these segments is approximately 150 feet long. When the lowest step is within 150 feet of a positively charged object, the positive charge reaches it, generating an electric current (in the image, the visible lightning is indicated in yellow).
Other types of lightning, the most frequent, never leave the clouds, but travel between differently charged areas within, or between them (cloud-to-cloud in the image).
Rarely, “positive” lightning strikes, which originates from the top of the storm clouds, positively charged. These lightning bolts have an inverted charge flow and are much more powerful and destructive. A positive lightning bolt can extend into the sky and hit the ground “out of nowhere”, more than 10 miles from the storm cloud in which it was born.
Lightning can be spectacular, but above all it is dangerous. Around 2,000 people are killed by lightning every year worldwide. Hundreds more survive the accident, but suffer from a variety of lasting symptoms, including memory loss, dizziness, weakness, numbness and other ailments that complicate life.
Cars are a great place to protect from lightning, as the tires conduct the current, as do the metal frames, which thus discharge electricity to the ground without causing any danger. Many houses are built to harmlessly conduct lightning electricity to the ground. Even plumbing systems, gutters or other materials can unknowingly help to discharge the current to the ground.