The Sciences

Artificial Lightning

Fire in the MindBy George JohnsonMar 1, 2013 3:45 PM

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Makeshift rocket launchers on South Baldy Peak. Photo by George Johnson. When I was writing Fire in the Mind, the book this blog is named after, I almost included a chapter about lightning. One of my aims in the book was to explore the edges of science's map of the world, and I was fascinated that something as commonplace as a thunderstorm remains so little understood. In the end the science of lightning didn’t make it into my book, and I didn’t take up the subject again until years later when National Geographic asked me to write the story about Tim Samaras, the lightning chaser I described in my previous post. It was only then that I got to spend time at the Langmuir Laboratory for Atmospheric Research on South Baldy Peak and witness a spectacular experiment. It is the nature of journalism that some of the people who help most with a story end up with only bit parts or are not included at all. That is what happened with most of the crew at Langmuir, so I am glad to have a chance to resurrect this unpublished account. . . . as I drove up a winding dirt rode to the Langmuir Laboratory for Atmospheric Research in the Magdalena Mountains of New Mexico, I thought about something Bill Winn, the laboratory’s director, had said on the telephone the day before: “Tim Samaras chases lightning. We wait for it to come to us.” And sometimes they manage to summon it from the sky. Imagine Ben Franklin’s legendary experiment but with a rocket instead of a kite and a long wire in place of the string. Fire the rocket into a highly charged cloud and, if you’re timing is right, the result is artificially induced lightning. Built in 1963 on a ridge just below South Baldy Peak by the New Mexico Institute of Mining & Technology in Socorro, the laboratory sits in the path of the monsoonal moisture that flows up from the Gulf of Mexico each summer. As I arrive, Elissa Eastvedt, a master’s degree student, is on top of Baldy mounting half a dozen small, remote-controlled rockets onto their launch pads. The pads are simple affairs, each consisting of a vertical plastic pipe supporting a rod to hold the rocket and an ordinary metal mailbox to shield the circuitry from electromagnetic noise. (Otherwise a pulse from a lightning flash might cause a rocket to fire accidentally.) At the base of the launch pad, a spool called a bobbin holds hundreds of meters of wire -- enough for several experiments. When the rigging is complete, Eastvedt takes cover in an underground metal bunker -- the Kiva -- and waits to fire the rockets into a thunderstorm that is approaching from the southwest. About a mile away, inside an observation room on top of a building called the Annex, the rest of the team -- Ken Eack, an Assistant Professor of Physics at Socorro, and Harald Edens, who is working on his PhD. -- are looking back toward the Kiva as the familiar colored radar blobs glide across a computer screen. Electric field meters like the one on Samaras’s trailer show an increasing atmospheric charge, and occasionally we hear a beep from an optical lightning sensor. “Kiva is on storm status,” Eastvedt reports by radio. “Two point two kilovolts per meter.” A siren warns everyone on the mountain to take cover. Five point two, five point seven -- the field climbs higher and higher until, just as conditions seem promising, a natural lightning flash discharges the sky. As we wait for the atmosphere to recharge, Eack talks about the advantages of studying lightning in captivity rather than in the wild: you can surround it with instrumentation. Because it consists of moving electrical charges, lightning generates electromagnetism -- from low-frequency radio waves to high-frequency x-rays. Detectors mounted at the Kiva and at the Annex record these emanations while a Phantom camera captures imagery. Like Samaras’s high-speed videography, the data from Langmuir might help address a longstanding puzzle. For all their intensity, the voltages produced in thunderclouds are not nearly high enough to overcome the insulating properties of the air. To spark a lightning strike some additional factor is required. X-rays might be a clue, indicating the presence of a phenomenon called “runaway breakdown,” in which an avalanche of electrons, moving at almost light speed, overcomes the air’s electrical resistance. But that poses another problem: what produces the high-speed electrons? Lightning itself is not powerful enough. Some theorists suggest that the particles may be triggered by cosmic rays. Just before 5 p.m. we’re interrupted by the radio: “If the radar is right we’re about to get hammered,” Eastvedt says. A few minutes later her wish comes true. “This is the Kiva to the Annex. Requesting a launch window.” Eack scans the mountain with binoculars to be sure there are no hikers nearby, then gives permission to fire when ready. The first attempts are disappointing -- one rocket produces lightning, but the image is obscured by thick clouds. As the storm grows more violent, lightning is flashing so close to the peak that it knocks out power to the Kiva. “Good Lord!” Eastvedt says when she recovers from the thunder clap. “That was the loudest one I’ve ever been here for.” With only three rockets left and the Kiva now on battery backup, her chances are diminishing. Then: “Kiva launch in five.” Four, three, two, one . . . Suddenly a bright column of light appears on top of Baldy -- the wire tethered to the rocket being vaporized by an upsurge of electricity. Almost instantly a second streak appears to ricochet off the top of the column -- the artificial lightning -- and into the sky. It all happens so fast that it’s hard for the brain to untangle. Later a slow-motion video shows the details: the illuminated wire looking at first like a string of beads then becoming solid and brighter; the jagged secondary streamers that dance for an instant around the main corridor of light; the repeated pulsations as multiple return strokes follow the path of charged air -- so much complexity packed into half a second. After the storm passes and the electric field drops to safe levels, Eack and I get into an old military Jeep and ascend the switchbacks to the Kiva where Eastvedt and Winn are observing the damage from the day’s work. Lightning has burned little holes in one of the mailboxes, and a screw on a wire bobbin has become welded to the frame. As I prepare to leave, lightning still flickers in the distance and a rainbow appears, its reds amplified by the setting sun.

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