With ultra-fast cameras, and assets that are in the right place at the right time, physicist Marcelo Saba National Institute for Space Research (Inpe)and doctoral student Diego Rhamon obtained an unprecedented image of a lightning discharge, showing details of its connection to several nearby lightning rods.
The image’s rarity has earned it the cover of Geophysical Research Letters (GRL), one of the region’s foremost scientific journals. This work was supported by FAPESP.
“This picture was taken on a summer night, in sao jose dos campos [SP]when the downward negatively charged rays approach the ground at a speed of 370 kilometers per second,” Saba said.
“Just a few tens of meters away from the ground, many lightning rods and the cornices of buildings in the area produced upward positive discharges, which competed with the downward lightning. The final image before the connection was the lightning strike. 25 millionths of a second before a building,” he continued.
GRL’s editors reproduced this spectacular image on the publication’s cover.
His camera can capture 40,000 images per second, the researchers report. Shot in super slow motion, the video shows the lightning rod in action. Lightning can also be dangerous if these protective devices are not properly installed.
That’s because, despite more than 30 lightning rods nearby, the lightning wasn’t connected to any of them, but to the chimney of an oven located on top of one of the buildings.
“A failed installation left the area unprotected. The 30,000-amp strike did impressive damage,” he said.
Watch for a moment:
Images captured by ultra-high-speed camera show how lightning rods work Images captured by ultra-high-speed camera show how lightning rods work
On average, 20 percent of lightning strikes are made up of the exchange of electric charge between the cloud and the ground. The remaining 80% consists of discharges within the cloud.
Of the rays that touch the ground, nearly all are descending rays: they start in the cloud and reach the ground. Upward rays also exist, but are rare. They only occur in tall structures like hilltops, skyscrapers, towers, and antennas. Depending on the charge they transfer to the ground, lightning can be further classified as negative or positive.
“Lightning can be up to 100 kilometers long. And carry about 30,000 amperes. That’s the equivalent of 30,000 100-watt light bulbs working together. In some cases, the current can reach 300,000 amperes. The temperature of lightning is 30,000 °C, which is five times the surface temperature of the sun,” Saba said.
how rays are formed
It all starts with the electrification of the cloud, the researchers explain. Its mechanism is not fully understood. But roughly speaking, it stems from friction between ice particles, water droplets and hailstones, releasing charges and creating polarities between different regions of the cloud, with potential differences ranging from 100 million to 1 billion volts.
“It is necessary to consider that storm clouds are huge structures with bases 2 or 3 kilometers above the ground and tops that can reach a height of 20 kilometers. Their diameters are between 10 and 20 kilometers,” he said.
The explanation for the branching form that the rays take is that the charge seeks the easiest path, the path of less resistance, rather than the shortest path, the straight line.
The simplest path, usually a zigzag, is determined by the different electrical properties of the atmosphere, which is not uniform. “The light beam consisting of multiple discharges lasts for up to 2 seconds. However, each discharge lasts only a fraction of a millisecond,” Saba added.
He pointed out that lightning rods neither attract nor repel lightning. It also didn’t release clouds as previously thought. It just provides an easy and safe path to ground for lightning.
Since it is not always possible to rely on lightning rod protection, and summer is when most atmospheric discharges occur, it is convenient to consider Saba’s advice. “Storms happen more in the afternoon than in the morning.
So pay attention to outdoor activities on summer afternoons. When you hear thunder, seek cover. Never stand under trees or utility poles. Even under the crappy cover.
If you don’t have a sturdy place to protect yourself, stay in your car and wait out the storm. If there is no car or any other place to shelter from the rain, squat down with your feet together. Never stand up, never lie down. In the house, avoid touching electrical appliances and using corded phones.”
People struck by lightning can survive, researchers claim. And there are many such examples. The chances increase when the person is cared for promptly. “Cardiac arrest is the only cause of death. In this case, the recommended care is CPR”, he taught.
Saba started systematic research on lightning in 2003 using high-speed cameras. The research, which is still ongoing, provides the world’s largest library of high-speed lightning videos. The researcher and his advisor have been considered for 17 grants or grants from FAPESP.
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