Rare lightning bolt images from Brazil detail how rods work
A rare image detailing a lightning strike showing connections to nearby rods was captured by a researcher in Sao Paulo using a set of high-speed cameras installed on top of high-rise buildings.
The image, a combination of a well-planned effort and luck (the right place at the right time) revealed details of the lightning strike's corona brush, streamers, and space stems.
The activity was spearheaded by Marcelo Saba, a researcher at Brazil’s National Space Research Institute (INPE), and Diego Rhamon, a Ph.D. candidate. According to his team, the image featured a negatively charged lightning bolt nearing the ground at 370 kilometers per second.
"When it was a few dozen meters from ground level, lightning rods and tall objects on the tops of nearby buildings produced positive upward discharges, competing to connect to the downward strike, said Saba in a press release.
The final shot before the connection was obtained 25 thousandths of a second before the lightning struck one of the buildings.
The image was featured on the cover page of the December edition of the journal Geophysical Research Letters, along with an article related to the research. Saba began studying lightning with high-speed cameras in 2003, building one of the largest databases of videos of lightning filmed at high speed.
Advanced equipment that detailed the lighting discharge
The team made use of a camera that captures 40,000 frames per second. The high-speed equipment allowed researchers to evaluate the impact of such strikes, especially when adequate protective measures are not followed. In this specific case, a fault in the installation had exposed the area, and the impact of a 30,000-amp discharge did substantial damage.
"A staggering total of 31 lightning precursor channels (called leaders) were launched from nearby buildings in an attempt to intercept the downcoming negative leaders."
Lightning strikes can also be classified as negative or positive depending on the charge transferred to the ground. It is estimated that only 20 percent of the lightning strike make contact with the ground, the rest getting confined in the clouds.
According to the team, such strikes can be as long as 100 kilometers and transport currents as strong as 30,000 amps. "The temperature of a typical lightning strike is 30,000 degrees Celsius, five times the Sun’s surface temperature," said Saba.
High-energy discharge produced during lightning strikes
Lightings are formed due to the friction between ice particles, water drops, and hail, releasing charges and creating polarities between different cloud regions. Such electrical potentials can range from 100 million volts to 1 billion volts.
Due to electrical charges' quest to follow the path of least resistance, lighting strikes branch out, usually following a zigzag pattern rather than a straight line. "Its path is determined by different electrical characteristics of the atmosphere, which is not homogeneous."
According to the team, lightning rods do not repel or attract such electrical discharges but merely provide lightning an easy and safe route to the ground. According to the team, vulnerable people, especially those who work outside during summer afternoons, are advised to take shelter.
The full study was published in Geophysical Research Letters and can be found here.
A very close high-speed video observation of lightning attachment to a building revealed novel details regarding the leader streamer zone dynamics. Upward leaders propagate in a steady and unbranched manner, displaying a uniformly luminous corona brush. The exception being the upward connecting leader (UCL) just before connection, when its streamer zone increases in size and develops a more filamentary pattern. Downward negative leaders have 3-m long multiple streamers emanating from each negative leader tip. On some occasions, plasma formations known as space stems are seen to form in the location previously occupied by negative streamers. Space stems have luminosities comparable to the main leader channel, but are detached from it by 4 m. Some space stems display streamers of their own, including cases where streamers are emanating from both ends. The space stem formation hampered the propagation of the negative leader that was closest to the UCL.