With a high-speed camera and the luck of being in the right place at the right time, physicist Marcelo Saba, a researcher at the National Space Research Institute of Brazil (INPE) and Ph.D. candidate Diego Rhamon obtained a unique lightning image showing details of connections to nearby buildings.
The image appeared on the cover of the Dec. 28, 2022 issue of Geophysical Research Letters (GRL) which contained an article with Saba as first author.
“The image was captured on a summer evening in So Jos dos Campos [in So Paulo state] while negatively charged lightning was approaching the ground at 370 km per second. When it was only a few dozen meters above ground level, lightning rods and tall objects on the tops of nearby buildings produced upward positive discharges, competing to connect to the downward strike. The final image before the connection was obtained 25 thousandths of a second before the lightning struck one of the buildings,” Saba said.
He used a camera that shoots 40,000 frames per second. When the video plays in slow motion, it shows how lightning strikes behave and also how dangerous they can be if the protection system is not installed correctly: although there are more than 30 lightning rods nearby, the lightning is not connected to them but to a chimney on top of one of the buildings. “A flaw in the installation left the area unprotected. The impact of a 30,000 amp discharge caused massive damage,” she said.
On average, 20% of all lightning strikes involve an exchange of electrical discharges between the clouds and the ground. The other 80% occur within clouds. Nearly all shots that hit the ground are cloud-to-ground discharges. Upward shots also occur, but are rare and begin atop tall structures such as mountains, skyscrapers, towers, and antennas. Lightning can also be classified as negative or positive, depending on the charge transferred to the ground.
Lightning strikes can be up to 100 km long and carry currents of up to 30,000 amperes, equivalent to the current drawn 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 30,000C, five times the surface temperature of the sun,” Saba said.
How lightning is formed
It all starts with the electrification of the cloud, he explained. The mechanism is poorly understood but basically involves friction between ice particles, water droplets and hail, releasing charges and creating polarity between different cloud regions, with electrical potential differences ranging from 100 million volts to 1 billion volts .
“Keep in mind that storm clouds are huge structures. The lower part is 2-3 km above the ground, the upper part can reach 20 km in altitude, and the diameter can be between 10 and 20 km,” he said.
Lightning strikes as electric 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 the different electrical characteristics of the atmosphere, which is not homogeneous. “A bolt of lightning composed of multiple discharges can last up to 2 seconds. However, each discharge lasts only fractions of a millisecond,” Saba said.
Lightning rods neither attract nor repel strikes, he added. Nor do they “dump” clouds, as was believed. They simply offer lightning an easy and safe path to earth.
As protection from a lightning rod cannot always be relied upon and most lightning strikes occur in summer in the tropics, Saba’s advice is worth considering. “Thunderstorms are more frequent in the afternoon than in the morning, so watch out for outdoor activities on summer afternoons. Find shelter if you hear thunder, but never under a tree or post, and never under a rickety roof,” he said .
“If you can’t find a safe place to shelter, stay in your car and wait out the storm. If there is no car or other shelter available, squat down with your feet together. Do not stand or lie down. In closed environments, avoid contact with household appliances and landline telephones.”
It is possible to survive a stroke of lightning, and there are many examples. The odds increase if the person gets treatment quickly. “Cardiac arrest is the only cause of death. In this case, cardiopulmonary resuscitation is the recommended treatment,” Saba said.
Saba began systematically studying lightning with high-speed cameras in 2003, and has since built a collection of high-speed lightning videos that has become the largest in the world.