American and European physicists were able to answer the long-standing question of what exactly causes a bolt of lightning in the clouds.
To do this, they used the LOFAR Low-Frequency Array, which consists of thousands of small radio telescopes, originally intended for astronomical observation and developed by Dutch engineers.
Brian Hare, a lightning researcher at the University of Groningen in the Netherlands, and one of the authors of the new article. It is very difficult to visually study the process of lightning formation, since thunderclouds are opaque. Meteorological balloons and rockets recently gave scientists a chance to study the interiors of clouds, but their presence inside clouds distorts the data, artificially creating sparks that would not have appeared naturally.
Now it’s radio astronomers’ tools to help researchers. LOFAR’s Array of Radio Telescope was originally designed to study distant galaxies and exploding stars, but it turns out great for studying Earth’s lightning as well.
During imaging, it turned out that pre-emergent lightning generates millions of random radio pulses, but almost all of them come from a small area 70 meters deep within the thunderclouds.
One theory was that lightning strikes could be caused by cosmic rays – high-energy particles from space that collide with electrons within the cloud, thus causing electronic avalanches that amplify electric fields.
Researchers have now been able to confirm a theory that it all starts with clusters of ice crystals inside a cloud. Turbulent collisions between crystals allow some of the electrons to be discarded, while one end of each ice crystal becomes positively charged, and the other – negative. Paths of ionized air lead to the streamers, one of which eventually turns out to be hot and conductive enough to turn into a conductor – an atmospheric channel through which a whole powerful lightning bolt can travel.
The major role of ice crystals in these processes is consistent with the recent finding that lightning activity on the planet decreased by more than 10% during the first three months of the COVID-19 pandemic. Researchers attribute this decrease to a decrease in the amount of pollutants in the air, and thus to a decrease in the number of areas where ice crystals can form.
