Scientists find clues to the mystery of what causes lightning - It's well-known that lightning is an electric current—a quick, powerful burst of charge that flows within a cloud or between a cloud and the ground. But surprisingly, scientists still don't fully understand how the initial spark forms that generates such powerful lightning.
In a new paper published in Nature Communications, researchers from Langmuir Laboratory at the New Mexico Institute of Mining and Technology near Socorro, New Mexico, have reported observations of a rare but extremely powerful type of lightning spark, or discharge, called narrow bipolar events. The scientists found that this powerful type of lightning is caused by a newly recognized type of discharge called fast positive breakdown, and the data suggests that this same discharge initiates most or even all of the lightning flashes typically seen in thunderstorms. These sparks travel at speeds that are fast even for lightning—around 10 to 100 million meters per second—and produce very powerful radiofrequency (RF) radiation as high as a few megawatts, making them the strongest natural sources of RF radiation on Earth.
This discovery is surprising, since previous simulations have shown that lightning breakdown appears to be negative, meaning the spark moves upward in the cloud from a negative to a positive region. In positive breakdown, the spark moves downward from a positive to a negative region.
"It is impossible to simulate thunderstorm conditions in a conventional laboratory," coauthor William Rison at the New Mexico Institute of Mining and Technology told Phys.org. "The sparks in thunderstorms are hundreds of meters to kilometers long, a scale that is orders of magnitude larger than in any laboratory environment. Theorists have been trying to simulate these conditions in computer experiments, and the most plausible results have suggested that the sparks are initiated with relativistic electron avalanches, which is a type of negative breakdown. Our results clearly show that the initiation is with a positive breakdown, not a negative breakdown."
The results could help scientists better understand how a cloud can generate a current that is powerful enough to cause lightning. Currently, the largest electric fields that have been measured inside thunderstorms are several times weaker than what is needed to break down cloudy air and initiate lightning.
In general, lightning occurs when the positive and negative electric charges in a cloud separate in different parts of the cloud. Charge separation sets the stage for lightning to form either between the negative and positive parts of the cloud (intracloud lightning), or downward to the ground (cloud-to-ground lightning), where it often strikes a tree, telephone pole, or other tall object.
In a new paper published in Nature Communications, researchers from Langmuir Laboratory at the New Mexico Institute of Mining and Technology near Socorro, New Mexico, have reported observations of a rare but extremely powerful type of lightning spark, or discharge, called narrow bipolar events. The scientists found that this powerful type of lightning is caused by a newly recognized type of discharge called fast positive breakdown, and the data suggests that this same discharge initiates most or even all of the lightning flashes typically seen in thunderstorms. These sparks travel at speeds that are fast even for lightning—around 10 to 100 million meters per second—and produce very powerful radiofrequency (RF) radiation as high as a few megawatts, making them the strongest natural sources of RF radiation on Earth.
This discovery is surprising, since previous simulations have shown that lightning breakdown appears to be negative, meaning the spark moves upward in the cloud from a negative to a positive region. In positive breakdown, the spark moves downward from a positive to a negative region.
"It is impossible to simulate thunderstorm conditions in a conventional laboratory," coauthor William Rison at the New Mexico Institute of Mining and Technology told Phys.org. "The sparks in thunderstorms are hundreds of meters to kilometers long, a scale that is orders of magnitude larger than in any laboratory environment. Theorists have been trying to simulate these conditions in computer experiments, and the most plausible results have suggested that the sparks are initiated with relativistic electron avalanches, which is a type of negative breakdown. Our results clearly show that the initiation is with a positive breakdown, not a negative breakdown."
The results could help scientists better understand how a cloud can generate a current that is powerful enough to cause lightning. Currently, the largest electric fields that have been measured inside thunderstorms are several times weaker than what is needed to break down cloudy air and initiate lightning.
In general, lightning occurs when the positive and negative electric charges in a cloud separate in different parts of the cloud. Charge separation sets the stage for lightning to form either between the negative and positive parts of the cloud (intracloud lightning), or downward to the ground (cloud-to-ground lightning), where it often strikes a tree, telephone pole, or other tall object.
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