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A technical look at lightning

If caught outdoors, you want to be as short as possible and have as little contact with the ground as possible

I was having a hard time coming up with a weather article for this week. (Remember, feel free to email me any questions or topic ideas that you have at [email protected]) As I sat down to write, a line of severe thunderstorms developed and pushed through my region. The storm didn’t have much in the way of severe weather, but did produce a lot of lightning. According to my Boltek lightning detector the storm, at its peak, was producing over 1,500 lightning strikes every minute! This got me thinking about lightning, so I checked back over the articles I’ve written and it has been a few years since I last wrote in detail about lightning. So for this week’s article, I thought it would be good to take a look at how lightning is thought to form, and then take a look at some lightning facts and safety tips.

For this discussion we’ll look at a typical lightning strike that starts in the cloud and hits the ground. First of all, lightning is caused by a build of electrical charge within a thunderstorm. It’s believed strong up-and-down drafts within a thunderstorm cause particles of dust, water and ice to hit each other. These millions of collisions allow for electrons to be transferred between particles, causing these particles to become charged. This is a very similar process to the one that gives you a charge when you drag your feet across a carpet in the winter. Within the thunderstorm, these same up-and-down drafts separate the charged particles into regions, so some areas of the storm become negatively charged, while other areas positively charged. Exactly how this happens is still not completely understood.

When an area of the storm gains a strong-enough charge, it will act on the air around it, causing it to ionize (the air molecules break apart, forming positive and negative atoms). This ionized air can now conduct electricity. Meanwhile on the ground, the strong negative charge in the clouds above the earth pushes electrons (which are negative) away. In objects that are good conductors (metals), electrons move easily so these objects become strongly positive; this makes them more attractive to the negative charge in the cloud. You can sometimes see this when you’re outside just before a thunderstorm. If someone’s hair starts to stand up, that means the individual strands of hair have become charged, and since they have the same charge, they repel each other and begin standing up. By the way, this is not a good thing, so even though it seems cool and funny, it should tell you there is a very strong charge in the clouds above you!

As objects on the ground become more and more positive they begin to send out what’s known as positive streamers. These positive streamers reach out toward the cloud, trying to make a connection. At the same time, a step leader is moving down from the cloud. This is a narrow channel that is coming down from the base of the cloud, forming a zigzag pattern as it builds towards the ground. This step leader or channel fills with electrons as it makes its way to the ground. Once the step leader gets close to the ground, the positive streamers try to connect up with it. Once one of them does make the connection, the channel is complete and all the electrons can now flow. This whole process, up to this point, will typically take about one second.

The electrons in the channel that are closest to the ground will begin to flow first, followed by electrons farther and farther up the channel. As these electrons flow, they bump into particles of air, transferring some of their energy in the form of heat. This causes the air to heat up and glow. Since the electrons flow from the bottom up, it may appear the lightning originated from the ground, even though it originated in the cloud. If there is a large-enough charge in the cloud, we may see two or three “dumps” of electrons down the original channel. On the ground we would see this as a multiple flash of lightning.

Now, on to some lightning safety information and facts. The average lightning bolt is about two centimetres wide and 7.5 km long, but lightning bolts can be as long as 40 km, with the record length being 190 km. These long bolts of lightning often come out the side of the storm and can hit the ground a long distance from the storm. This is where the term “bolt out of the blue” comes from.

As far as safety is concerned, there is no truly safe place from lightning if you get caught outdoors. If you are caught outdoors with no shelter available, you want to minimize two things. First of all, you want to be as short as possible, and secondly you want to have as little contact with the ground as possible. To accomplish this, you can squat on the balls of your feet, tucking your head down with your hands over your ears. Luckily most of us will never find ourselves in this situation! If you have shelter nearby, the 30/30 rule is the easiest one to remember. The first 30 means that if you see lightning and then count to 30 or less before you hear the thunder, it is time to head in for shelter. The second “30” means you should wait 30 minutes after the last rumble of thunder before heading back outside. This second one can be tough, but just remember that bolt out of the blue!

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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