Lightning is a massive electrostatic discharge between regions of opposite electrical charge — typically within a cumulonimbus cloud (intra-cloud lightning, ~75 % of all flashes) or between the cloud and the ground (cloud-to-ground lightning, ~25 %). A single bolt can carry 200–300 million volts and heat the air to approximately 30,000 °C — five times hotter than the sun's surface — producing the characteristic flash and the shock wave we hear as thunder.
The charging mechanism involves collisions between ice crystals and graupel (soft hail) in the strong updrafts of thunderstorms. Lighter ice crystals carry positive charge upward; heavier graupel carries negative charge to the mid-levels, creating a charge separation of billions of coulombs. When the electric field exceeds the insulating capacity of air (~3 MV/m), a stepped leader (invisible, branching channel) reaches toward the ground. As it approaches, a return stroke surges upward through the channel — this brilliant flash is what we see, occurring in under a millisecond.
Lightning kills an estimated 2,000 people worldwide annually and injures ten times more. It causes wildfires (lightning is the leading natural ignition source), damages infrastructure, disrupts aviation, and triggers power outages. Spain records approximately 2–3 million cloud-to-ground strikes per year, concentrated in the spring–autumn thunderstorm season and in mountainous areas. Modern lightning detection networks (like AEMET's) locate strikes in real time with accuracy of 200–500 m, enabling warnings. Satellites like the Lightning Imaging Sensor provide global coverage, revealing Earth's lightning hotspot: Lake Maracaibo, Venezuela, with ~297 lightning days per year.