A rare high-speed photograph of lightning showing connections to nearby lightning rods is helping scientists understand how these devices compete to attract lightning strikes and keep buildings safe from damage.
The image, which was made possible through a combination of well-planned effort and sheer luck, was captured during a thunderstorm in Sao Jose dos Campos, Brazil, with a high-speed camera by physicist Marcelo Saba, a researcher at the National Institute for Space Research (INPE) of Brazil, and doctoral student Diego Rhamon.
Lightning rods released upward discharge to attract lightning
According to the researchers, who published their analyzes in Geophysical Research Letters, the image shows a negatively charged lightning bolt approaching the ground at 370 kilometers per second. When the lightning was about 30 meters above the ground, “lightning rods and tall objects on top of nearby buildings produced upward positive discharges, which competed to connect with the downward impact” explained Saba in a FAPESP statement.
“The final image prior to connection was obtained 25 thousandths of a second before the lightning struck one of the buildings,” added Saba.
The researchers used a camera that captures 40,000 frames per second. The high-speed equipment allowed the researchers to assess the impact of these types of downloads, especially when proper protection measures are not followed. In this specific case, a failure in the installation had exposed the area, and the impact of a discharge of 30,000 amperes caused considerable damage.
“A staggering total of 31 precursor channels of lightning (called leaders) were launched from nearby buildings in an attempt to intercept the descending negative leaders.”
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Lightning, an electrifying nature
According to the press release, on average, it is estimated that only 20% of lightning strikes the ground, and the rest is confined to the clouds. Almost all lightning strikes that strike the ground are cloud-to-ground discharges. Upward discharges also occur, but are infrequent. Lightning can also be classified as negative or positive based on the charge transferred to the ground.
“Lightning strikes can reach a length of 100 km and carry currents as strong as 30,000 amps, equivalent to the current used simultaneously by 30,000 100-watt light bulbs. In some cases, the current can reach 300,000 amps. The temperature of a typical lightning strike is 30,000 °C, five times the temperature of the Sun’s surface,” explains Saba.
Because electrical charges seek to follow the path of least resistance to the ground, not the most direct path, lightning strikes have their characteristic zigzag shape. “Its trajectory is determined by the different electrical characteristics of the atmosphere, which is not homogeneous.”
According to the team, lightning rods neither repel nor attract such electrical discharges, but simply provide lightning with an easy and safe path to the ground.
According to the statement, Saba began systematically studying lightning with high-speed cameras in 2003, and has since created a collection of high-speed videos of lightning that has become the largest in the world.