Thunder
Overview
Thunder is a phenomenon in which the air surrounding a lightning discharge channel is instantaneously heated and expands rapidly, producing a shock wave that is transmitted as sound. It is a representative atmospheric acoustic phenomenon that accompanies thunderstorms, and the time difference from lightning can be used to estimate approximate distance.
Main Content
Mechanism
A lightning channel is heated to extremely high temperatures reaching tens of thousands of kelvins in a very short time. The air then expands explosively, pushing surrounding air and creating a strong shock wave. As the shock wave travels farther, it becomes a sound wave, which is the thunder people hear. Thunder can accompany lightning whether it occurs within a cloud, between clouds, or between a cloud and the ground, but the loudness and character of the sound heard vary depending on the location of occurrence and propagation path.
Characteristics of the Sound
Thunder may be heard as a single sharp bang or may continue as a long rumbling sound. When a lightning channel discharges multiple times along a tortuous path, sound can be produced multiple times, and reverberation occurs as sound reflects off terrain, buildings, and cloud layers. Thunder contains not only audible sound but also infrasonic components that can travel long distances.
Distance Estimation
The speed of sound in air is about 343 meters per second; at 20 degrees Celsius, it takes about 3 seconds to travel 1 kilometer. By counting the time between the lightning flash and the thunder and dividing by 3, an approximate distance can be obtained. However, this is only an approximation, and errors can occur depending on air temperature, wind, and terrain.
Meteorological Conditions
Thunder occurs mainly in strongly convective clouds such as cumulonimbus. Lightning and thunder become more frequent when updrafts are active, moisture is sufficient, and the atmosphere is unstable. It appears in continental thunderstorms in summer, tropical squalls, supercell storms, and other systems; dry thunder, in which rain does not reach the ground, can increase the risk of wildfires.
Safety Response
When thunder is heard, it means lightning has already occurred nearby, so one should immediately move to a safe indoor location. The widely used 30-30 rule advises that if thunder follows lightning within 30 seconds, the risk is high and one should take shelter. It is recommended to avoid outdoor activities for at least 30 minutes after the last thunder is heard. Avoid large playing fields, mountain tops, bodies of water, isolated trees, and metal structures, and take shelter inside a car or a sturdy building.
Culture and Language
Thunder has long symbolized the power and sacredness of nature. There are many cases in which thunder and lightning have been interpreted as divine power, such as Zeus in Greek mythology and Thor in Norse mythology. In Korean, thunder and lightning are mentioned together to metaphorically express sudden events or great shocks.
Scientific Measurement
In modern meteorology and atmospheric electricity, microphone arrays, infrasound sensors, lightning detection networks, and satellite observations are used to analyze thunder and lightning activity. By tracing thunder's acoustic signals backward, the discharge location and energy characteristics can be estimated, and this is also used for aviation safety, disaster alerts, and wildfire monitoring.
Recent Trends
In 2024-2025, research is active on combining artificial intelligence with satellite and radar data to predict the likelihood of thunderstorms and lightning risk more quickly. The influence of urban heat islands and climate change on the frequency and intensity of strong convective storms is also a major topic. Smartphone-based lightning reports, infrasound detection networks, and real-time disaster alert services are expanding as means of delivering thunder and lightning risk information to citizens.
Related Topics
- [[Lightning]]
- [[Thunderstorm]]
- [[Atmospheric electricity]]
- [[Meteorology]]
- [[Climate change]]