Question: Where does lightning come from?

Cloud to cloud lightning in Zwickau, Germany. By André Karwath, via Wikimedia Commons

Thanks Ashlynn from Adelaide for being my first asker!

Most of us have no doubt had the experience of getting little electric zaps from walking in sneakers on some carpets, or taking off a woolly jumper. If you have fuzzy synthetic blankets you’ve almost certainly seen them, too!

These little sparks happen when certain materials rub against each other. Lightning works a similar way, just on a dramatically larger scale.

To create the conditions for lightning, we need an area with extra positive electric charge and an area with extra negative electric charge. In a storm cloud, the top gets positively charged and the bottom negatively charged. These positive and negative charges come about from the droplets and ice crystals jostling against each other as they move around in the cloud. As they brush past each other, some can steal negatively-charged pieces called electrons from others. The electron thieves gain negative electric charge, and the particles the electrons were stolen from become positively charged.

The most likely reason for the negatively charged particles ending up at the bottom and the positively charged ones at the top seems to be that the electron-thieves tend to be heavier particles, and the electron-losers lighter particles.

Electric charge does not like to stay built up in one place. When there is a large enough amount of separated positive and negative electric charge, it can literally tear electrons off air molecules to force the air to temporarily conduct electricity.

The process of tearing away electrons from the air molecules causes the air molecules to emit light. The path the electricity takes through the air therefore lights up, and we see lightning.

Lightning can happen within the cloud, as in the picture, making a path between the negatively charged bottom and the positively charged top of the cloud.

The negative charges in the bottom of a cloud can also push away the electrons in things in the ground, making them more positively charged. This separation between positive and negative can also be bridged by tearing up air molecules, giving lightning strikes between clouds and the ground.


I hope that helps!

If you want to know more, think I’ve made a mistake, or have a completely unrelated question, please comment here or jump across to my Ask a Question page to let me know what you’re thinking!


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