Text: Bizarre' lightning strike to be studied Art Thomason The Arizona Republic Aug. 11, 2005 12:00 AM A top National Weather Service expert in Phoenix will investigate a powerful lightning strike that "sounded like dynamite exploding," damaging 13 homes in central Mesa on Tuesday afternoon. "This is beyond the norm," meteorologist David Runyan said. "It's bizarre. It intrigues us. We will seek some means to understand it a little more." The lightning bolt drawing all the attention caused extensive damage to a home in the 2000 block of East Seventh Avenue, near Broadway and Gilbert roads, as its charge sped to other structures through underground wiring and wet soil. Mesa firefighters, who have seen the aftermath of other lightning strikes over the years, said they have never witnessed anything like the effects of the Seventh Avenue strike. ... The force's intense heat exploded underground wires, including television cable, near the home, erupted through the soil and spewed dirt and debris like volcanic ash against homes, trees and parked vehicles. Areas around brass doorknobs and locks were scorched. [snip] On Wednesday, Runyan, of the Weather Service, said he would visit the site after Randall Cerveny, an assistant professor of meteorology at Arizona State University, indicated it could have been hit by a positive strike, which is extremely rare and powerful. Scientists say positive strikes deliver much more voltage than the negative bolts that occur 90 to 95 percent of the time in storms across the country. Positive strikes also tend to spread their potent charge over a larger area. "They tend to be much more powerful," Cerveny said. "We don't know much about them because they are so rare." How far the strike spreads depends on such factors as how much underground wiring is in the area and if the ground is wet. "The strike follows the path of least resistance, such as wiring," Cerveny said. But Ron Holle, a meteorologist who studies lightning for Global Atmospherics Inc. in Tucson, isn't convinced yet that the strike was positive. "It could have been a lightning flash with multiple return strokes," he said. "Between the strokes, there is a continuing current, and it doesn't stop. We have no idea why it happens." One thing is sure, the scientist agreed. Arizona's recent monsoon storms have produced far more lightning strikes than normal.

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