léidiàn

Léidiàn (雷电) refers to the natural atmospheric electricity phenomena commonly known in English as lightning and thunder. Lightning is a rapid discharge of electricity that occurs during thunderstorms, producing a bright flash. Thunder is the sound generated by the rapid heating and expansion of air along the discharge channel.

Lightning results from charge separation within and between cumulonimbus clouds and, in many cases, between a cloud and the Earth's surface. Updrafts and collisions between precipitation particles cause the upper portions of a cloud to become positively charged and the lower portions negatively charged. When the electric field becomes strong enough to overcome air's insulating properties, a breakdown occurs. A conductive channel, often starting with a stepped leader from the cloud and a connecting stroke from the ground or another region, allows a return stroke to travel upward, creating a bright flash. Lightning can be cloud-to-ground, intra-cloud, or cloud-to-cloud; ground-to-cloud discharges are rare.

Thunder is produced by the extreme heating of the air along the lightning channel, which can reach tens of thousands of kelvin. The rapid expansion creates a shock wave heard as thunder. Because sound travels much slower than light, thunder is heard after the flash, with the delay giving an approximate distance: about 0.3 to 0.4 seconds per 100 meters.

Global lightning activity averages roughly 1.2 to 1.4 billion flashes per year, with higher frequency in tropical and subtropical regions. Lightning can affect the environment by initiating wildfires and contributing to atmospheric chemistry, including nitrogen oxides and ozone formation.

Safety and protection measures include seeking shelter indoors during storms, avoiding tall isolated objects outdoors, unplugging sensitive electronics, and utilizing proper building lightning protection and grounding systems.