Lightning patterns found in storms.

Lightning pattern found in storms

Atmospheric scientists have discovered that in many thunderstorms, the most dangerous lightning develops on only one side of the storm instead of striking randomly throughout the entire area. This observation will aid those who are studying the development of thunderstorms, and may provide a warning system for locating potentially damaging parts of a storm.

Using a large network of instruments that monitor individual lightning flashes, researchers from the State University of New York at Albany found that many storms, especialy during the fall and winter, display an unexpected organization. At the downwind end of the storm, most lightning flashes are positive charge from the cloud to the ground. Meanwhile, 100 kilometers away at the rear of the storm, most flashes lower negative charge to ground.

Richard E. Orville and his colleagues discovered this so-called bipolar pattern when they linked several small lightning- detection networks. "The pattern has been there, but we've never had a lightning network large enough to observe it," Orville told SCIENCE NEWS. Orville, Ronald W. Henderson and Lance F. Bosart report their findings in the February GEOPHYSICAL RESEARCH LETTERS.

Scientists have measured electrical currents in positive lightning that are sometimes twice as strong as those found in negative lightning. If scientists can predict where positive lightning is likely to occur, they can forecast which areas of a thunderstorm will be the most hazardous.

The Albany scientists speculate that horizontal winds may help cause the bipolar arrangement in storms. Individual thunderclouds normally have a vertical organization with positively charged tops and negatively charged bottoms. But observations have shown that when horizontal winds develop at the level of the cloud top, the cloud begins to tilt, with the positive charge drifting downwind.

Over time, suggest the researchers, this drift would build a center of positive charge at the downwind end of the storm, leading to positively charged lightning in that area.

Such a theory, however does not explain the entire phenomenon. Horizontal winds are normaly too slow to carry enough charge to the storm front. The researchers believe that another mechanism may help generate teh positive- charge center. In future studies they will address this issue by combining satelite and radar data with records from the lightning network.