Clues to mystery of what causes lightning found

Scientists have observed a rare but extremely powerful type of lightning spark which could help them better understand how a cloud can generate a current that is powerful enough to cause lightning.
Researchers from New Mexico Institute of Mining and Technology found that this powerful type of lightning called narrow bipolar events, is caused by a newly recognised type of discharge called fast positive breakdown.
Data suggests that this same discharge initiates most or even all of the lightning flashes typically seen in thunderstorms, researchers said.
These sparks travel at speeds that are fast even for lightning - around 10 to 100 million metres 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, they said.

"The sparks in thunderstorms are hundreds of metres to kilometres long, a scale that is orders of magnitude larger than in any laboratory environment," William Rison from New Mexico Institute of Mining and Technology told 'Phys.Org'.
"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," said Rison.
The results could help scientists better understand how a cloud can generate a current that is powerful enough to cause lightning, researchers said.
The findings were published in the journal Nature Communications.