There can be lightning without hearing thunder primarily because thunder is a sound that travels much slower than light and can dissipate or be blocked before reaching the observer. This phenomenon is often called "heat lightning."
Reasons for Lightning Without Thunder
- Distance: Thunder typically cannot be heard beyond about 20 miles (32 kilometers). Lightning flashes, however, can be seen from much farther away, sometimes up to 100 miles or more depending on terrain and atmospheric conditions. So, when lightning is too far away, the thunder sound dissipates before reaching the observer.
- Speed Difference: Light from lightning travels almost instantaneously to the observer, while sound (thunder) travels at about 343 meters per second (about 741 miles per hour). The delay means that if the thunder arrives after a significant delay or is faint, it might not be perceptible, or the observer might not connect it with the lightning flash.
- Atmospheric and Environmental Effects: Atmospheric layers with different temperatures and densities can bend or refract sound waves upward or away from the observer, reducing or eliminating the sound of thunder reaching certain locations. Terrain, vegetation, and buildings can also absorb or block sound, and weather conditions like rain or snow can dampen it further.
Summary
Lightning always produces thunder because it heats the air explosively, creating a shockwave. However, if the lightning strike is too distant, or if atmospheric conditions alter the sound's path, the thunder may not be heard, leading to the perception of lightning without thunder, commonly termed as "heat lightning".
This means seeing lightning without hearing thunder does not mean there is no thunder; it simply means the thunder sound waves did not reach the observer.
