Lightning, weather’s byproduct, may become a predictor
Lightning’s intricate, darting dance across the sky can be mesmerizing or terrifying, elegant or explosive, divine or destructive, depending on how close it is.
But meteorologists have historically viewed lightning as little more than a weather byproduct. Like a rainbow, only with teeth.
That view may be changing as technology has evolved to study lightning and its potential to help predict, if not drive, atmospheric events. In 2017, two new space-based lightning sensors are set to go live, joining a growing global architecture of groundbased detection networks (some making their images available for free online). “We are now in the golden age of lightning measurement and research,” said Christopher Schultz, a meteorologist and lightning specialist at the Marshall Space Flight Center in Huntsville, Ala.
Worldwide, thunderstorms hurl about four million lightning bolts to the ground each day. So it’s not surprising that researchers have spent decades figuring out how to track and measure the phenomena, and trying to persuade funding sources that collecting data was worthwhile.
“When I got started back in the ‘80s, nobody cared,” said Hugh Christian, a research professor at the University of Alabama at Huntsville and director of the team that developed a lightning sensor that will be attached to a truss of the International Space Station in 2017. It will augment coverage provided by a geostationary satellite, known as GOES-16, that was successfully launched in November.
“It’s been a long road,” Christian said. “But now it’s universally accepted that lightning flash rates are correlated with storm intensification and severity.” This means the more that is known about lightning activity, the more advance warning it is possible to give people about the possibility of associated severe weather events like tornadoes and hail.
Experts hope to locate about 90 percent of lightning strikes in the Western Hemisphere, within clouds and on the ground, using detection instruments in space that work by measuring photons blinking in the clouds below and, terrestrially, by sensing radio wave disturbances.
European and Japanese lightning-sensing satellites are expected to launch within the next five years, making similar data collection possible worldwide.
Researchers have also discovered different and strange iterations of lightning. For example, so-called dark lightning, powerful bursts of gamma rays (strong enough to produce antimatter), can smash through the upper regions of Earth’s atmosphere and into outer space. This has implications for the functioning and longevity of satellites used for communication, military reconnaissance and GPS.
“It’s totally unexpected and exciting that thunderstorms can turn into something like giant particle accelerators,” said Joseph Dwyer, a professor of gamma ray astronomy at the University of New Hampshire. “And we found lightning is initiating it.”
Other surprising and mysterious sorts of lightning are elves and sprites — colorful ultrafast bursts of electricity that dance above clouds into the upper atmosphere.
“We’re getting pretty good at saying what lightning does, but we’re still pretty bad at saying how it does it,” Dwyer said. “It’s so common and yet we really don’t understand it very well.”
The current thinking is that ice particles in different forms within thunderstorms bump up against one another during updrafts and transfer charges (similar to what happens when you walk across a carpet and touch a doorknob). The lighter particles get positively charged and migrate to the top of the cloud, while the negatively charged, heavier particles drop to the bottom.
The negative buildup at the bottom of the cloud discharges to the positively charged ground below, or upward or sideways, depending on the easiest path for release. The same thing can happen with the accumulated positive charges if a certain threshold is met for discharge.
“The problem is people have been sending up balloons and airplanes into thunderstorms for decades, and the measured electric fields are nowhere big enough to create a spark,” Dwyer said. “So how does lightning get started inside thunderstorms? It’s one of the biggest mysteries in the atmospheric sciences.”