"Lightning" - what is it, definition of the term
A rapid, high‑voltage electrical discharge that develops within a cloud, between separate clouds, or between a cloud and the Earth's surface, releasing a sudden burst of energy that generates a bright flash, a thunderous acoustic shock, and ionization of the surrounding atmosphere.
Detailed information
Electrical discharge in the atmosphere originates when strong electric fields separate positive and negative charges within clouds. The separation occurs through collisions of ice particles, water droplets, and graupel, producing regions of opposite polarity. When the field strength exceeds the breakdown threshold of air, a conductive channel forms, allowing a rapid flow of electrons from the negatively charged area to the positively charged one. This process releases intense light, heat, and acoustic energy.
Key characteristics of the phenomenon include:
- Peak temperature exceeding 30,000 °C, sufficient to vaporize surrounding air and create a plasma channel.
- Current amplitudes ranging from a few kiloamperes to several hundred kiloamperes.
- Duration of the visible flash typically 1–5 ms, while associated sound waves travel at the speed of sound and may be heard seconds later.
Several distinct forms are recognized:
- Cloud‑to‑ground discharge: a downward channel connecting a charged region in the cloud to the Earth's surface.
- Intra‑cloud discharge: horizontal or vertical channels confined within a single storm system.
- Cloud‑to‑air discharge: upward flashes that terminate in the surrounding atmosphere rather than the ground.
- Positive polarity flash: originates from the upper part of the storm, carrying a higher voltage but lower current than the more common negative discharge.
Safety considerations focus on avoiding conductive pathways. Metal objects, tall structures, and water increase risk. During a storm, the recommended actions are to seek shelter indoors, stay away from windows, and avoid contact with plumbing or electrical appliances. If caught outdoors, crouch low, minimize contact with the ground, and keep hands away from the head.
Measurement techniques rely on electric field sensors, fast optical detectors, and radio‑frequency antennas. Data from these instruments enable estimation of charge transfer, energy release, and the spatial geometry of the plasma channel. Such information supports weather forecasting, aviation safety, and the design of lightning‑protection systems for buildings and infrastructure.