April 30, 2008 -- For the first time, a laser has been used to trigger electrical activity in a thunderstorm -- or not. It turns out that the success or failure of the experiment, reported in the April issue of the journal Optics Express, depends on who you ask.
The experiment in question involved the use of the world's most powerful portable laser, which was taken atop the 10,500-foot South Baldy Peak in New Mexico in 2004. From there it shot super-fast laser pulses at two passing thunderstorms.
The pulses were manufactured to resemble the rapid-fire electrical activity inside the same clouds, as observed in 3-D by researchers at the New Mexico Institute of Mining and Technology's Langmuir Laboratory.
"It can be compared to a metal stick," explained Jérôme Kasparian of the University of Lyon in France, referring to the way strong lasers can create short-lived filaments of lightning-inducing ionized air. Kasparian is the lead author of the report.
Laser pulses "are able to ionize the air over a long distance and we were for the first time able to initiate electrical activity," he said.
In other words, Kasparian claims to have triggered not lightning but a lesser sort of electrical activity inside thunderstorm clouds that might be a precursor to lightning. Kasparian compared the lesser electrical activity to ball lightning -- what's often called St. Elmo's Fire -- forming at the end of the laser.
In the end, Kasparian's declaration of success was based on a statistical correlation between the laser shots and the lightning observations. But statistics can be tricky and troublesome.
"I was shocked to see it on international news," said another lightning researcher who spoke to Discovery News on the condition that his name not be used. The Optics Express report conclusions are simply not true, he said. "At the time (in 2004), the experiment was deemed a failure."
Other prominent researchers who are very familiar with the experiment also disagree with Kasparian's conclusions. They told Discovery News that they are planning to respond directly to the journal and preferred not to comment in detail outside of scientific circles.
That said, the foremost question mark on Kasparian's experiment is whether or not his laser just lucked onto electrical activity that was already underway. In other words: Was it a coincidence?
"As pointed out in the original article," responded Kasparian, "less than 1 percent of the laser pulses triggered an event. However, the statistical analysis has been conducted according to classical procedures and shows high confidence levels, precisely at the laser beam location."
Such a statistical result is considered acceptable in most fields of science, he said, even with few events.
Among the other difficulties include the differences in how natural lightning and laser-induced electrical discharges might look to the Langmuir Lab lightning detection system.
Messy electrical discharges are usually thrown out when data are analyzed. But Kasparian included them in his statistical analysis because they represent just the kind of signal he expects from multiple discharges along a laser beam. This is sort of a Catch-22 that makes some researchers uncomfortable.
About the only thing everyone agrees on is that a lot more work is needed before lasers can begin bringing lightning to the ground. Finally mastering that ability should help in the study of thunderstorms, as well as in developing technology to deliberately bleed off lightning from clouds so that aircraft and sensitive structures are not struck.
Right now the only effective method to trigger cloud-to-ground lightning is with tethered rockets. In this method, scientists use rockets connected to the ground by wires. They fire the rockets into clouds and trigger electrical discharges.
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