The Mystery Behind Lightning
Zeshan Nisar (Bloger)
A discharge of atmospheric electricity, accompanied by a vivid flash of light, commonly from one cloud to another, sometimes from a cloud to the earth. The sound produced by the electricity in passing rapidly through the atmosphere constitutes thunder.
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.
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 radio frequency (RF) radiation as high as a few megawatts, making them the strongest natural sources of RF radiation on Earth.
Atmospheric scientists have a basic sketch of the process. Positive electric charges build up at the tops of thunderclouds and negative charges build up at the bottoms except for perplexing patches of positive charges often detected in the center bottom. Electrical attraction between these opposite charges, and between the negative charges at the bottom of the cloud and positive charges that accumulate on the ground below, eventually grow strong enough to overcome the air's resistance to electrical flow.
One theory holds that high energy cosmic rays from space shoot down through the cloud, stripping off electrons from atoms as they go and dragging these negatively charged particles toward the cloud base, creating a charge imbalance. Dwyer said that although this process may play a role, it doesn't seem sufficient to explain the huge imbalance that scientists observe.
Lightning is also a useful tool. For example, some research shows that lightning might offer a long-distance measurement of total rain rate, allowing for precipitation monitoring in otherwise unobservable regions. Los Alamos has also used lightning signals as “probes” that can map small structures in the Earth’s ionosphere.
These radio frequency signals from lightning that we typically observe from space give us a bird’s eye view of the whole earth. So might we someday use space based lightning detection to globally predict tornadoes and other severe weather events, with enough lead time to prevent casualties. We’re not there yet, but could be someday.