What happens when the CN Tower is struck by lightning?

Whether you love them or hate them, thunderstorms are an exciting weather phenomenon, even more so at the CN Tower! Lightning typically strikes the tallest object in the area of a thunderstorm, and the CN Tower is certainly the tallest point in Toronto! But have you ever wondered what happens when the CN Tower is struck by lightning?

Image of lightning

Well, to understand that, we should first look at how lightning works. A thunderstorm cloud is a collection of millions of tiny water droplets. As water droplets, ice pellets, or snow flakes, in clouds rise and fall, they bump into each other. The larger droplets can steal electrons, the negatively charged particles in every atom, from smaller droplets, and become negatively charged. Atoms and molecules try their very hard to remain neutral, with an equal number of positive and negative charges. With fewer electrons, the smaller droplets become positively charged.  With the help of wind and gravity, these positive and negative charges separate between the top and the bottom of the cloud, creating a charge separation. This causes an electric field to form inside the cloud, like the poles of a magnet. And much like a magnet’s poles, the same electric charges don’t like each other. The negative electrons in the ground are repelled by the increasing electric field in the storm cloud, creating a localized positive charge in the ground. When the accumulated charge in a storm cloud is large enough, the air around it begins to ionize. This sudden release or freeing of electrons creates an ideal path for charge to flow between the cloud and the ground. Actually, the lightning moves both ways, with a positive streamer from the ground joining a step leader from the cloud. The electrical charge in the cloud releases its energy down into the ground as lightning.

The CN Tower is well prepared for a lightning strike. A series of copper strips run the length of the Tower. Copper is very conductive and allows electrons to move easily through it. These strips feed into massive grounding rods buried below ground level. When lightning does strike the Tower, the electrical discharge runs through the wires and diffuses into the ground. And don’t worry, this system has been put to the test! On average, the CN Tower is stuck by lightning 75 times per year!

Fun Facts:

The Tower may be the tallest object in Toronto, but the tallest thing isn’t always struck by lightning. Where lightning happens to strike is a complex process…For example, during the construction of Ripley’s Aquarium, Guests and Tower team members reported seeing lightning strike the construction cranes in and around the growing Aquarium. These cranes were at least 300m shorter than the CN Tower! Why this happens is very difficult to answer. It could be that the crane was affected by the storm cloud’s electric field more quickly than the Tower, resulting in a stronger positive charge and an easier path to the ground. More metal in the crane, or more surface area, because most cranes are long, interconnected trusses. Whatever the reason, it was a spectacular experience, from a very unique vantage point!

Want to learn more? Check out these source links:

How Stuff Works - How Lightning Works
National Weather Service - Lightning Safety
National Geographic - Lightning Facts
Lightning Maps