Volcanic Eruption's Green Lighting Explained By Atmospheric Scientist

redOrbit Staff & Wire Reports – Your Universe Online

Mysterious green lightning, seen emerging from an ash cloud in images of a May 2008 volcanic eruption in Chile, is likely more common than we realize, according to research presented Monday during the annual fall meeting of the American Geophysical Union in San Francisco.

Green lightning had not really been observed before photographer Carlos Gutierrez snapped photographs of the Chaiten volcano eruption, according to Olive Heffernan of National Geographic. The origin of the unusual phenomenon was unknown until Arthur Few, an atmospheric scientist and professor emeritus at Rice University, began investigating the unusual climatic event.

“I thought, ‘That’s funny; why don’t we see this in lightning storms?’” Few said during the conference. Despite the fact that the Chaiten eruption is known to have given off visible green lighting, Few believes that the phenomenon is not all that unusual, said Larry O’Hanlon of Discovery News. He believes that it is more common than people realize, but is most likely hidden inside of regular thunderstorms.

“The concealment results from the structure of storm clouds,” Heffernan said. “On the inside, the clouds contain ice crystals that are either positively or negatively charged. Surges of electricity occur between positively and negatively charged regions within the cloud – lightning – but they remain inside, unseen by even the most committed storm chasers. In contrast, volcanic ash clouds carry their electrical charges on the outside, where they are sparked by fragments of rock forcefully ejected into the air during an eruption.”

What Few doesn’t understand, and is currently attempting to find out, is why the ash column produced during the Chilean eruption produced visible green lighting. For answers, he looked at other atmospheric phenomena which appear to be green, such as the northern lights. The aurora glows green, red and white when their oxygen atoms are excited by electrons originating from space. Above 100 km, the northern lights appear to be green.

“My working hypothesis is that the green ones are actually streamers,” Few explained. Streamers are lightning bolts which are effectively “a positive channel being pulled to a negative charge” occurring higher up in the ash cloud. Essentially, the white lightning visible in the Chaiten pictures is a negative charge generating throughout the cloud and curving into its bottom, while the green lighting is the positive streamer that reverses the flow, O’Hanlon said.