April 25, 2013
Dark Lightning And Its Visible Counterpart May Be Related, Say Researchers
Watch the video "Scientists Detect Dark Lightning Linked To Visible Lightning"
Brett Smith for redOrbit.com - Your Universe OnlineDiscovered in 1991, dark lightning is an electrical phenomenon that occurs deep within a thunderhead and is responsible for producing a powerful burst of radio waves and gamma rays. Now, new research from an international team of scientists has found that dark lightning and visible lightning may be connected, according to a report in Geophysical Research Letters.
“Our results indicate that both these phenomena, dark and bright lightning, are intrinsic processes in the discharge of lightning,” said lead author Nikolai Ãstgaard, a space scientist at the University of Bergen in Norway.
Using information collected from a pair of satellites, the researchers found instances of dark lightning´s signature gamma ray flash and radio wave discharge immediately before seeing a bolt of visible lightning. In their report, the team suggested that the burst of dark lightning — also known as a terrestrial gamma flash — was released by a powerful electric field that formed just before the onset of visible lightning.
The observation stems from a unique chance occurrence in 2006 when two independent satellites flew within 186 miles of a Venezuelan storm. Both satellites, one fitted with an optical detector and the other equipped with a gamma ray sensor, were able to collect distinct data on the storm´s electrical activity.
Last year, Ãstgaard and his colleagues said they found the previously undetected gamma ray burst while reanalyzing the two sets of satellite data.
“We developed a new, improved search algorithm “¦ and identified more than twice as many terrestrial gamma flashes than originally reported,” Ãstgaard said. “It was fortuitous that two independent satellites — which are traveling at 7 kilometers per second (4.3 miles per second) — passed right above the same thunderstorm right as the pulse occurred.”
The satellites´ observations along with radio-wave data that was recorded 1800 miles away at Duke University allowed the team to reconstruct the electrical event that led to both lightning flashes.
According to the report, a strong electric field developed immediately before the visible lightning, creating a surge of electrons moving at almost the speed of light. When the electrons collided with surrounding air molecules, the event released a burst of gamma rays and lower energy electrons that are characteristic of dark lightning.
Ãstgaard believes there could be an intrinsic connection between terrestrial gamma flashes and visible lightning, but he stressed that additional research needs to be done to verify this theory.
Some have noted the dark lightning´s gamma rays can expose airplane passengers to harmful neutrons that have been ℠excited´ away from oxygen in the air or aluminum in an aircraft.
Marco Tavani, an astrophysics researcher at the University of Rome who was not involved in the latest study, said that neutrons can be “pretty nasty,” and flyers are already being exposed to higher levels of neutrons then they would be on the ground.
He added that the bursts of neutrons generated by thunderstorms are not as well understood.
Officials have already made plans to further investigate the dark lightning phenomenon. The European Space Agency´s“¯Atmospheric Space Interactions Monitor (ASIM) is scheduled to launch within the next three years, and researchers say it will be able to better detect both types of lightning from space.