Stay inside during thunderstorms

8 juli 2021

Dark sky with lightning

Every year five or six people come into contact with lightning in Sweden. One research speciality at Uppsala University is how to protect oneself against thunder.

If you hear thunder, don’t go outside. This is the most important piece of advice from lightning researcher Vernon Cooray. Death by lightning is highly unusual in Sweden, but caution is called for at this time of year. At Uppsala University, research is under way on how to protect oneself from both lightning and thunder physics.

Cooray, Professor of Electricity at Uppsala
University. Photo: Mikael Wallerstedt

In Sweden, thunderstorms are more common in the summer. This is because the thunder (cumulonimbus) clouds need strong heat at ground level so that the air rises up high and creates thick clouds. These, in turn, generate lightning flashes.

“The thicker the cloud, the more strikes there are. What’s needed to generate flashes of lightning is heat, but also humidity in the air to create thunderstorms. That's why we get thunderstorms in summertime, when various parts of Sweden start heating up, and why there are more thunderstorms in the south of Sweden than in the north,” Vernon Cooray says.

Cooray, Professor of Electricity at the University’s Department of Electrical Engineering (Division of Electricity), has been doing research on thunder and lightning for 40 years. He and his colleagues have a standard piece of advice when it comes to protecting yourself from thunder.

“If you hear thunder, don’t go outdoors. That’s the best way to protect yourself from lightning strikes. Usually, the probability of anybody being killed by lightning in Sweden is very, very small,” he says.

“That’s because in this country, the frequency of thunderstorms isn’t very high, and people are really aware of the danger of thunderstorms. Most people take precautions.”

Five or six victims a year

A person getting struck by lightning is a rare event in Sweden, but every year five or six people come into contact with it somehow. It might be that lightning strikes close to them; it may, for instance, hit a nearby tree and they may be touched by part of the lightning that passes along the tree.

“Usually they don’t die, but in the worst case they may become unconscious. They go into shock, and may not remember what happened. If you get a direct strike, through your head for instance, the risk of dying is very high. Most of the time, somehow, the lightning just grazes us.”

“The most frequent types of damage caused by lightning are due to fires. But the probability of lightning strikes is extremely low,” Cooray says. Photo: Mikael Wallerstedt

Most buildings, such as large apartment complexes, are constructed out of concrete reinforced with metal. So remaining indoors in such housing is like staying inside a cage.

“A metal cage is the best protection from lightning. For example, if you’re inside a car and it’s completely made of metal, it’s safe. However, nowadays you also find plastic in cars.”

Fire risk without lightning protection

For people who live in detached (single-family) homes, there is a risk of the building catching fire if there is no lightning protection device, such as a rod or conductor. The most frequent cause is lightning getting into the electrical system and burning down cables and creating a short circuit, so that it starts a fire in the house.

“The most frequent types of damage caused by lightning are due to fires. But the probability of lightning strikes is extremely low, so many people don’t have any lightning protection – myself included. I hope for the best,” Cooray says with a laugh.

Research on thunder and lightning has been in progress at Uppsala University since 1930, but to this day much is still unknown about this weather phenomenon. One research speciality is how to protect our buildings and structures against lightning. It is all about being able to predict where lightning will strike if you set up various structures next to one another, but also how to protect electrical power systems against the damaging effects of lightning.

How does a lightning strike begin?

Cooray’s other research focus is the physics of lightning. What happens when lightning strikes and what are the effects?

“We still don’t know how lightning starts inside the thundercloud. In our high-voltage lab, we can use a metal electrode and apply a very high-voltage pulse to it – creating a mini lightning strike. But we still don’t know how this high voltage is created inside the cloud.”

There are two different theories. One is that the needed voltage will arise during the collisions between water droplets, ice crystals and hail, the other theory assumes that lightning is triggered by cosmic radiation.

“In our high-voltage lab, we can use a metal electrode and apply a very high-voltage pulse to it – creating a mini lightning strike,” Coray explains.

Besides experiments in their high-voltage lab, Uppsala scientists use a research facility in Switzerland. This is a 100-metre-high tower located in the mountains, at an altitude of 2,500 metres, that is struck by lightning about 100 times a year.

“We’ve sent our equipment there to measure the X-rays and gamma rays generated by the lightning. The Swiss researchers have facilities to see what happens inside the thundercloud, so when we combine these, we’ll get a good idea of how lightning is initiated.”

New instruments prompt new questions

Another vital research question is how lightning generates X-rays and gamma radiation. In experiments in the high-voltage lab, X-rays can be measured. But the question is, how does it arise?

So there’s still a lot you don’t know?
“That’s the strange thing. After doing this research for the last hundred years, you might think that we’d know everything about thunderstorms and lightning. But time passes and new equipment is developed. Every time you aim a new instrument at a thundercloud, you find something new,” Cooray says.

Using radio waves, the researchers are trying to understand what happens inside a thundercloud. This research is taking place in collaboration with tropical countries, such as Sri Lanka, where thunderstorms are more common than in Sweden.