What Causes Lightning Bolts?

Everyday Einstein explains the mechanics of lightning and thunder.

Lee Falin, PhD
3-minute read
Episode #61

Nothing strikes fear in the hearts of children like a house-shaking thunderstorm. Lightning flashes, thunder rumbles, and children scream in terror. Since nothing helps dispel fear like understanding, let’s take a look at some of the science involved in thunder and lightning.

See also: Dogs and Thunderstorms;

Fast as Lightning

While we don’t understand everything about lightning, here are some things we do know. Lightning is like a giant spark of static electricity. Particles of ice smash into one another inside of storm clouds, breaking apart and picking up electrostatic charges. The lighter, positively charged particles gather near the top of the clouds, while negatively charged particles gather near the base.

What happens next depends on lots of complicated factors. One possibility is that once the voltage is high enough, an electrostatic discharge occurs between the two regions of the same cloud, forming what is called intra-cloud lightning.

Sometimes, the discharge can occur between the positively charged region of one cloud, and the negatively charged region of another. This is called inter-cloud lightning.

The kind of lightning most of us are familiar with is called cloud-to-ground lightning. Though a more accurate name would be cloud-meets-the-ground-halfway-lightning, but that isn’t anywhere near as catchy.

In cloud-to-ground lightning, the electrostatic charge occurs between the cloud and the ground. It’s a rather complicated process, but it starts with electrical “leaders” forking out from the cloud towards the ground in random, jagged steps. Once these steps get close enough to the ground, electrical “streamers” start to extend from objects on the ground towards the charge coming from the cloud.

Once the leader and streamer connect, a massive electrical charge flows from the cloud into the ground, producing the bright flash called the “return stroke” which we most commonly associate with lightning. The rest of the process is visible as well, but it happens so fast that it’s difficult to see.

One interesting fact is that while the charges flow from the cloud to the ground in the return stroke, the flow starts at the bottom and drains out from bottom to top. If you held a container of water up in the air and poked a hole in the bottom, the water would flow out the same way that electrical charge travels in the return stroke.


Please note that archive episodes of this podcast may include references to Everyday Einstein. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.