With a high-speed camera and the luck of being in the right place at the right time, physicist Marcelo Saba, researcher at Brazil’s National Institute for Space Research (INPE), and Ph.D. candidate Diego Rhamon obtained a unique image of lightning strikes that shows details of the connections to nearby buildings.
The image appeared on the cover of the December 28, 2022 issue Geophysical Research Letters (GRL)which contained an article with Saba as the first author.
“The photo was taken on a summer evening in São José dos Campos [in São Paulo state] while a negatively charged lightning was approaching the ground at 370 km per second. When it was a few dozen meters from ground level, lightning rods and tall objects on top of nearby buildings produced positive upward discharges, which competed to connect to the downstrokes. The last image before the connection was taken 25 thousandths of a second before the lightning struck one of the buildings,” said Saba.
He used a camera that takes 40,000 pictures per second. When the video is played in slow motion, it shows how lightning charges behave and also how dangerous they can be if the protection system is not installed correctly: Although there are more than 30 lightning conductors nearby, the impact did not connect to them but to a chimney on top of one of the buildings. “A fault in the installation left the area unprotected. The impact of a 30,000 amp discharge did enormous damage,” he said.
On average, 20% of all lightning strikes involve an exchange of electrical discharges between clouds and the ground. The other 80% occurs inside clouds. Almost all strikes that touch Earth are cloud-to-ground emissions. Upward strokes also occur, but are rare and begin at the top of tall structures such as mountains, skyscrapers, towers, and antennas. Lightning strikes can also be classified as negative or positive, depending on the charge transferred to the ground.
“Lightning strikes can be as long as 100 km and carry currents as strong as 30,000 amperes, equivalent to the current used simultaneously by 30,000 100-watt light bulbs. In some cases, the current can reach 300,000 amperes. The temperature of a typical lightning strike is 30,000 °C, five times the sun’s surface temperature,” Saba said.
How lightning strikes are formed
It all starts with cloud electrification, he explained. The mechanism is poorly understood but basically involves friction between ice particles, water droplets and hail, releasing charges and creating polarities between different cloud regions, with differences in electrical potential ranging from 100 million volts to 1 billion volts.
“Remember that storm clouds are huge structures. The bottom is 2 km to 3 km from the ground, the top can reach 20 km in height and the diameter can be 10 km to 20 km,” he said.
Lightning strikes branch out as the electrical charges seek the path of least resistance, rather than the shortest path, which would be a straight line. The path of least resistance, usually a zigzag, is determined by different electrical properties of the atmosphere, which is not homogeneous. “A lightning strike consisting of several discharges can last up to 2 seconds. However, each discharge lasts only fractions of milliseconds,” said Saba.
Lightning rods neither attract nor repel strikes, he added. They don’t “let go” of clouds, as people used to think. They simply offer lightning an easy and safe path to the ground.
Since it is not always possible to rely on the protection of a lightning conductor, and most atmospheric discharges occur in summer in the tropics, it is worth considering Saba’s advice. “Thunderstorms are more common in the afternoon than in the morning, so be careful with outdoor activities on summer afternoons. Take shelter if you hear thunder, but never under a tree or pole, and never under a rickety roof,” he said.
“If you cannot find a safe place to take shelter, stay in your car and wait for the storm to pass. If no car or other shelter is available, squat down with your feet together. Do not stand upright or lie flat. Indoors avoid contact with appliances and landlines.”
It is possible to survive being struck by lightning, and there are many examples. The odds increase if the person receives treatment quickly. “Cardiac arrest is the only cause of death. In this case, cardiopulmonary resuscitation is the recommended treatment,” said Saba.
Saba began systematically studying lightning with high-speed cameras in 2003, ever since building up a collection of videos of lightning filmed at high speed that has become the world’s largest.
More information:
Marcelo MF Saba et al, Close-up of Lightning Attachment Process Reveals Streamer Zone Fine Structure, Geophysical Research Letters (2022). DOI: 10.1029/2022GL101482
Journal information:
Geophysical Research Letters