[Physics] What determines the shape of lightning?

electromagnetismeveryday-lifegeophysicslightning

Everyone's seen lightning streaks, either in real life or in pictures and videos.

My question is, why does it look the way it does? Does lightning spread in a random manner, or is there physics behind the path lightning streaks trace in the sky?

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Best Answer

Your assumptions are right. There is indeed physics involved in lightning shapes.

Why can’t lightning just be in a plain, straight shape?

From the Indiana Public Media's Moment of Science Podcast episode "The Shape of Lightning Bolts":

The answer has to do with the complex way a lightning bolt forms. Although it looks like it forms all at once, a lightning bolt is actually produced in many steps. Instead of jumping right to the ground, the cloud’s negative charge begins with a short downward hop.

This initial hop is called a “leader,” and it’s no more than a few hundred feet long. From the lower end of this leader, another leader forms, and from the lower end of this, another. In this manner, the negative charge hops downward from leader to leader like a frog jumping from lily pad to lily pad across a pond.

While this is going on, the ground sends up its own chain of shorter, positively charged leaders. It’s only when these two chains meet, about a hundred feet off the ground, that we see the lightning bolt’s flash.

Lightning is jagged because each leader forms independently of the others. Each place a lightning bolt zigs or zags is where one leader stopped and another one started.

Each place a lightning bolt forks is where two separate leaders formed from the bottom end of a single leader above. This whole process takes only a few thousandths of a second, but that’s enough time to sculpt beautiful and complex lightning bolts.

Fun fact: Lightning is actually 5 times hotter than the Sun's "surface".

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