Why does thunder have different sounds?

AUSTIN, Texas (KXAN) — Have you ever wondered why thunder can have different sounds? A crack versus a rumble? Startlingly loud versus calmingly low? Let’s dive in …

The basics: what is thunder?

Electrical charges that build up in a storm release in the form of lightning. Extreme heat is generated by this electrical discharge with air surrounding the lightning channel superheating to around 54,000 degrees Fahrenheit (that’s about five times the surface temperature of the sun!)

All gases expand when the temperature increases, so when lightning superheats the air at just a fraction of a second, the air expands so rapidly that it compresses the air in front of it. Thunder is the acoustic soundwave generated by this quick expansion and contraction of air.

IN-DEPTH: A lightning bolt’s flash will always be seen before its thunder is heard because light travels faster than sound.

*Lightning is an electrical discharge. Thunder is the resulting soundwave from the rapid expansion & contraction of the air surrounding that channel of discharge.* (*Photo courtesy of the Bureau of Meteorology, Commonwealth of Australi*a)

What affects the sound of thunder?

Sound waves move faster in warm air compared to cold air and refract or bend towards areas of lower pressure. Since our atmosphere typically cools with height, these soundwaves tend to bend upwards, making it harder to hear thunder for a person farther away from the point of lightning. Moisture also plays a role as a more humid environment will bend or block more sound waves.

Sounds of thunder

A “crack” is typically indicative of a nearby or relatively close thunderstorm and/or with a strike perpendicular to a person (ex. lightning bolt stretching from the cloud to the ground).

A “rumble” is typically associated with storms further away and/or with a strike parallel to a person (ex. lightning bolt stretching from one end of a cloud to another).

A “boom” is indicative of a lightning strike reaching the ground.

A combination of “crack” & “rumble” is heard when sound waves from multiple strikes reach a person at varying times.

*Combination of perpendicular and parallel sound waves. COURTESY: Environment and Climate Change Canada (ECCC)*

Myth or not?

Lightning will never strike the same place twice.

MYTH. The Empire State Building in New York is said to be struck by lightning an average of 25 times a year.

If I can’t see the storm, I cannot get struck by lightning.

MYTH. Lightning can strike up to 10-12 miles away from its parent storm, given the term “bolts from the blue.”

I can survive a lightning strike.

TRUE. But impacts are likely. Ninety percent of people struck by lightning survive but often suffer long-term injuries.

Lightning safety

Every thunderstorm contains lightning, and safety is best achieved by staying inside when a storm is in the area. A building with four walls and a roof qualifies as “inside” (not a baseball dugout, not under an overhang or under a tree, etc.)

In 2022, Texas ranked #1 as the state with the most number of lightning strikes (27.7 million).

How does lightning strike a person?

There are five ways lightning can strike a person:

Direct strike – A person becomes a part of the lightning discharge channel.
Side flash – Lightning strikes a tall object and part of the current jumps to a person nearby.
Ground current – Lightning strikes an object and the energy travels outward in and along the ground surface.
Conduction – Lightning strikes metal or wiring, providing a path for the energy to follow.
Streamer – A downward moving lightning channel connects with what is called a streamer, a positively-charged channel of air right above a tall object on the ground. When a streamer makes a connection with the main channel, all nearby streamers discharge.

Click here for lightning strike animations.