"Thunder" - what is it, definition of the term
Thunder is the audible shock wave generated when a lightning discharge rapidly heats the surrounding air to temperatures around 30 000 °C, causing instantaneous expansion and creating a pressure pulse that propagates through the atmosphere as sound; the resulting acoustic event comprises a complex spectrum of frequencies, lasts from fractions of a second to several seconds, and varies in intensity with distance from the discharge source.
Detailed information
The acoustic phenomenon that follows a lightning discharge originates from rapid expansion of heated air. Temperatures can exceed 30,000 °C, causing a shock wave that propagates outward at supersonic speeds before slowing to the speed of sound. The resulting pressure pulse creates a sharp crack, often followed by a low‑frequency rumble as the wave reflects off terrain and atmospheric layers.
Key characteristics include:
- Peak overpressure reaching several kilopascals near the source, diminishing with distance according to an inverse‑square law.
- Frequency spectrum dominated by low frequencies (20–200 Hz) that travel farther than higher tones.
- Temporal structure composed of an initial “clap” lasting milliseconds, succeeded by a series of reverberations lasting several seconds.
Measurement relies on barometric microphones and high‑speed pressure transducers. Data are expressed in decibels relative to 20 µPa, with values above 120 dB capable of causing temporary hearing loss. Atmospheric conditions—temperature gradients, humidity, wind shear—modify wave speed and attenuation, influencing perceived intensity.
Biological impact extends to small arthropods. The sudden pressure change can:
- Displace ticks from vegetation, reducing host‑seeking activity.
- Disorient winged bugs, causing temporary loss of flight control.
- Interrupt the life cycle of lice by scattering eggs and nymphs across surfaces.
- Dislodge fleas from host fur, decreasing immediate infestation pressure.
Safety recommendations: seek shelter before the flash, avoid open fields, and protect hearing with earplugs if exposure exceeds 130 dB. Continuous monitoring of atmospheric electricity assists in forecasting the occurrence and severity of the acoustic event.