Over the last week or so, I finally saw some lighting in my area and, while I was not home at the time, I received a short but heavy pounding of hail. This got me thinking about thunderstorms and about lightning, so I checked back over the different weather articles I have written, and it appears that I didn’t go into much detail about lightning when I discussed the various severe summer weather threats. So, for this week’s article, I thought it would be good to look at how lightning is thought to form, and then 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, lightning is caused by a buildup of electrical charge within a thunderstorm. It is believed that strong up- and downdrafts 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 downdrafts separate the charged particles into regions so that some areas of the storm become negatively charged, while other areas are 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 pushes electrons (which are negative) away. In objects that are good conductors (like metals) the 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 are outside just before a thunderstorm. If the hair of someone 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 be telling you that there is a very strong charge in the clouds above you.
As objects on the ground become more and more positively charged, they begin to send out what is known as positive streamers. These positive streamers reach out towards 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, is filling with electrons as it makes its way down. 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 further and further 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 that 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 7-1/2 kilometres (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, then 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 latest safety saying adopted by both the American and Canadian weather agencies is: “When it roars, go indoors.” No more counting to estimate distances — if you hear thunder, it is time to pack it up and head indoors. Remember, even if it is clear overhead, there can still be that bolt out of the blue.