How to deal with a million bolts a month
Perhaps it was the effect of the silly season. In the first week of January this year Nomsa Dube, the KwaZulu-Natal minister for cooperative governance and traditional affairs, spoke about lightning. In less than two days, her statement went around the world, popping up as far afield as Japan and Brazil.
“We will do an investigation and talk to the department of science and technology on what is the cause of the lightning,” Dube said, at the site in Eshowe where seven people had died in a lightning strike shortly before.
The derision was swift and loud.
Anyone with a primary school education knows how lightning works and how to avoid being killed by it. What’s to investigate? But one group was notable for its absence from this mass-drubbing—the academics and researchers who understand lightning better than anyone. It turns out we don’t know nearly as much about it as you might expect.
By any measure there is a lot of lightning in South Africa. For the past four years the weather service has been pinpointing lightning strikes using a network of radio frequency detection sensors across the country, which have a better than 95% detection rate. In the peak summer season the number of flashes, or distinct bolts, has never dipped below a million a month.
The flashes are not equally distributed. The Western Cape has so few ground strikes they are barely worth counting, while parts of densely populated Gauteng and KwaZulu-Natal light up like a Christmas tree.
“South Africa is well known for the clustering of storms,” said Deon Terblanche, the weather services’ senior manager for research. “The combination of the density of strikes and the currents involved make us meteorologically high risk.”
South Africans also tend to be “outdoorsy”, and not always by choice. Travelling on foot or working in flat fields mean many are caught far from shelter when storm clouds gather.
Many more find themselves in informal or traditional dwellings, which provide little protection from lightning. Thatch roofs tend to catch fire when massive amounts of electricity are poured into them, while lightning can spark from a corrugated iron wall to a human body. Rural areas lack the underground network of pipes and wires that make city ground such a good, and safe, conductor.
But the biggest part of the risk equation is behaviour. Some people are just plain stupid. First prize goes to golfers who ignore thunder and warning klaxons and continue playing.
“We see more incidents at the beginning of the season,” said Estelle Trengove of Wits University. “People are more slapgat then and the ground is still dry, which makes it more dangerous to be near a strike.”
But there is a limit to just how paranoid you can be about lightning. Lightning bolts are known to travel horizontally for 30km or more before striking the earth. That means any storm that can be seen on the horizon, or heard to growl, is a potential killer.
But if tea pickers or construction workers in at-risk areas were to abandon work every time a thundercloud came within 30km, they’d spend much of their time twiddling their thumbs.
It seems South Africans tend towards the devil-may-care end of the spectrum—and these include people who know what they are up against.
“On a day like this I shouldn’t even run across the parking lot to get to my car,” said lightning safety expert Ryan Blumenthal, gesturing towards a dark, cloudy sky. “I also know that I’m going to do it.”
We don’t know exactly how many lightning deaths there are in South Africa but a conservative consensus puts the total at between 100 and 150 a year, with at least seven times as many injured.
That may or may not be a particularly high rate by global standards. Between the flimsy local data and the lack of numbers from areas like equatorial Africa, where storms go to party, nobody really knows.
What causes lightning?
And that’s not all we don’t know. Though the very basic science of lighting—charge separation takes place in clouds, with positive charge at the top and negative at the bottom, from where it occasionally finds its way to the planet’s surface—has been settled, it’s not that simple. Only in the past 20 years have atmospheric electricity researchers started to realise that lightning is bred from chaotic interactions, which is helping them understand why it can be triggered by seemingly low energy levels.
The gamma rays and antimatter produced by lightning storms are only now being observed and described. War is looming among meteorologists about whether global warming will cause a measurable increase in lightning activity, not to mention how climate change could affect the number of strikes in South Africa.
“We’re asking some fundamental questions about what is behind lightning that we previously answered in a very blunt way,” said Martin Füllekrug of the University of Bath. “We’re still working on what, in the end, causes lightning discharges to appear.”
Some of that kind of work has no practical benefit in the foreseeable future. Other lines of inquiry may find application in decades to come, such as local work on using laser pulses to ionise pockets of air and guide lightning strikes to a predetermined spot.
But the most startling research is into how lightning inflicts damage on humans and animals. Until 2002 there were four accepted mechanisms. Then two teams, one from South Africa, provided definitive proof beyond laboratory recreations of a fifth and rather scary addition.
On an October Sunday in 1998, Jomo Cosmos were 2-0 up in a PSL match against Moroka Swallows, with 15 minutes to go. Then, with many cameras recording the scene, there was a bright flash of light and several players fell to the ground, while others clasped their heads.
Researchers treasure the recording and have spent an enormous amount of time examining it. Their reconstruction showed two interesting things. First, even though lightning can branch near the ground and touch down in several places at once, none of the players was directly touched by a tendril of electricity. Second, at least four of the affected players had only one foot on the ground at the instant of the strike.
The streamer effect
When lightning hits the earth its energy radiates away from the impact point, with the electrical charge dissipating as it goes. Put two or more objects in that line of travel but a small distance apart, say the two legs of a human or the four of an animal, and the juicy flesh in between becomes the easiest path of travel for an electrical current. Electrical engineers refer to this as step potential and in 1998 it was the only one of the four known methods of lightning injury that didn’t require contact with a lightning strike or its subsequent stream of energy.
Two of the other three (a direct strike, or a side flash from a struck object such as a tree) are visible. The third, touch potential, requires the victim to be in contact with whatever conductor is carrying the energy, typically a wall.
But the soccer players writhing in agony had touched only the ground, and those with only one foot on it could not have fallen victim to step potential. The cameras had caught something new.
After studying the match tape Ian Jandrell, the head of the school of electrical and information engineering at Wits University, helped come up with the fifth mechanism—the upward streamer effect. “The most common lightning we see, about 90%, is negative-downward lightning,” Jandrell said. “There is a negative charge that travels down towards the earth, moving under its own steam in the classic zigzag pattern.
“We know it’s there but, until it makes contact with the earth, it’s invisible—you get the flash when it connects. As it gets close to the earth, a positive streamer starts to go upwards to connect to it. But you don’t just have one positive streamer, you can have many—many objects that are reaching out to that charge on its way down from the clouds.”
Think of it as a race in which there can be several participants—the bodies of the soccer players were taking part in the race. The positive streamers emanating from the tops of their heads lost the contest, then collapsed back into their bodies—with nasty consequences.
Like step potential, the streamer effect can kill entire groups near a strike, and higher surrounding structures don’t always afford protection.