Friday, March 16, 2007

Lightning may give information on volcanic activity

Lightning is the release of built up electrical energy in cumulus thunderclouds. As convection causes cumulus clouds to grow, particles in the upper levels freeze, separating positive and negative charges.Circulating air within the cloud further separates the charged particles, establishing a negatively charged base and a positively charged top.

Lightning results from the build-up and discharge of electrical energy between positively and negatively charged areas of the storm, and between charged portions of the storm and the ground.Volcanic ash clouds are similar to thunderclouds, which explains why lightning is often seen during large eruptions. In volcanic ash clouds, an electric charge is generated from the friction of ash particles expelled into the air, particle collisions and rock fractures.

Ash clouds from large eruptions are composed of particles of various sizes. Larger particles tend to be negatively charged and fall to the base of the cloud while smaller positively charged particles remain near the top, re-creating the same electric distribution seen in thunderclouds. As charges and particles build up, energy is released in the form of lightning.Lightning is the primary cause of forest fires in interior Alaska and is monitored by the Alaska Fire Service under the federal Bureau of Land Management.

Less than 20 small antennas monitor cloud-to-ground lightning across the state. The National Weather Service, National Oceanic and Atmospheric Administration, and BLM use this data in aviation forecasts, fire watches and general weather postings.Tom Dang, a meteorologist with the National Weather Service in Anchorage, said lightning-strike data is important in verifying weather conditions."Lightning reports and data are important for our forecasts," he said. "We don't have radar systems for the entire state, and the lighting reports confirm what is happening weatherwise in remote areas."McNutt is also trying to use lightning data as an indicator of volcanic activity.

"In poor weather conditions and at night, when wind and rain pound the ground disturbing our seismic instruments, we can look at lightning data and try to understand what's going on with the volcano and the ash clouds," he said.The published article just scrapes the surface of data collected from the 2006 Mount Augustine eruptions, McNutt said. He plans to continue working with the data to further define the relationship between electrical activity and volcanic ash cloud composition.Other UAF researchers involved in the article were Guy Tytgat and Edward Clark, who contributed technical support.

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