Gamma Rays Come From Some Thunderstorms

FEBRUARY 3, 2006 -- Research being conducted at Duke University's Engineering Department has helped discover that Gamma radiation is being emitted just before some lightning strikes in thunderstorms. According to Steve Cummer, one of those researchers, the Gamma-ray burst happens milliseconds before the electrical discharge.

Cummer says the discovery came about by accident in the mid-90s, when a satellite looking for Gamma-ray emissions from deep space picked up on something coming up from the earth. Over time, the researchers noticed that these Gamma-ray bursts were associated with cloud cover and then with thunderstorms.

At the Duke Forest in Orange County, Cummer and his fellow scientists use a low frequency radio (below the AM radio band) to detect the energy discharge from thunderstorms as far away as Africa. When their equipment finds a lightning strike, computers record the data, including the time of the lightning down to one one-thousandth of a second. Eventually it will be compared with data from satellites to see if a Gamma-ray burst corresponds with a lightning strike.

Cummer says that while it would seem that more electrically charged, and heavy lightning-producing thunderstorms, would seem to be the ones that would more likely produce these bursts of Gamma radiation, that's actually not the case.

"In fact, the lightning strikes that were connected with the Gamma-ray flashes were actually very modest. It even appeared to be on the small side of ordinary lightning strokes," Cummer adds.
Thunderstorms that are producing these Gamma-ray bursts occur mainly in the tropics, where the troposphere, the layer of the atmosphere where weather happens, is deeper. Cummer says there's no correlation between tropical cyclones and Gamma-ray producing thunderstorms. In fact, Cummer says, it's more of the isolated thunderstorms than anything else.

Reported by Mark Avery