A unique image captured by scientists using a high-speed camera shows how lightning rods work

The image, captured with a high-speed camera, shows several lightning rods attempting to connect to the downward discharge. Credit: Diego Rhamon/INPE

Armed with a high-speed camera and lucky enough to be in the right place at the right time, physicist Marcelo Saba, a researcher at Brazil’s National Space Research Institute (INPE) and Ph.D. Candidate Diego Rhamon received a unique image of lightning strikes, showing details of 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 first author.

“The picture was taken on a summer evening in São José dos Campos [in São Paulo state] while a negatively charged bolt of lightning approached the ground at 370 km per second. When it was a few tens of meters off the ground, lightning rods and tall objects on the roofs of nearby buildings created upward positive discharges that competed for connection with the downward strike. The last picture before 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 frames per second. When played in slow motion, the video shows how lightning discharges behave and also how dangerous they can be if the protection system is not properly installed: although there are more than 30 lightning rods nearby, the strike is not related to them but to a chimney on top of one of the buildings. “An error in the installation left the area unprotected. The effects of a 30,000 amp discharge did tremendous 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 within clouds. Almost all strikes that hit the ground are cloud-to-ground discharges. Upward strikes 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 up to 100 km long and carry currents of up to 30,000 amperes, which is equivalent to the current consumed by 30,000 100-watt light bulbs at a time. In some cases, the current can reach 300,000 amperes. The temperature of a typical lightning strike is 30,000 degrees Celsius, five times the surface temperature of the sun,” Saba said.

How lightning occurs

It all starts with the electrification of the cloud, he explained. The mechanism is poorly understood, but essentially involves the friction between ice particles, water droplets and hail, the release of charges and the generation of 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 to 3 km from the bottom, the top can be 20 km high and the diameter can be 10 to 20 km,” he said.

Lightning strikes branch when the electrical charges take 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 multiple discharges can last up to 2 seconds. However, each discharge lasts only fractions of a millisecond,” said Saba.

Lightning rods neither attract nor repel lightning, he added. They also do not “discharge” clouds, as was once believed. They simply provide lightning bolts with an easy and safe path to earth.

Since one cannot always rely on the protection of a lightning rod, and since most atmospheric discharges occur in the tropics in the summer, it is worth considering Saba’s advice. “Storms are more common in the afternoons than in the mornings, 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 can’t find safe shelter, stay in the car and wait for the storm to pass. If a car or other shelter is not available, squat down with your feet together. Do not stand up straight or lie flat. Avoid contact with devices and landline phones indoors.”

It is possible to survive a lightning strike, and examples abound. The chances increase if the person is cared for quickly. “Cardiac arrest is the only cause of death. In this case, CPR is the recommended treatment,” Saba said.

Saba began systematically studying lightning with high-speed cameras in 2003 and has since built up a collection of videos of lightning shots filmed at high speeds that has become the largest in the world.

More information:
Marcelo MF Saba et al, Close View of the Lightning Attachment Process Reveals the Fine Structure of the Streamer Zone, Geophysical Research Letters (2022). DOI: 10.1029/2022GL101482

Journal Information:
Geophysical Research Letters

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