Lightning may become one of weather's predictors

Lightning may become one of weather's predictors

Lightning’s intricate, darting dance across the sky can be mesmerising 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 ground-based detection networks. “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 Centre in Huntsville, Alabama, USA.

Worldwide, thunderstorms hurl about four million lightning bolts to the ground each day. So it is 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 1980s, nobody cared,” said Hugh Christian, a research professor at the University of Alabama at Huntsville, USA and director of the team that developed a lightning sensor that will be attached to a truss of the International Space Station in 2017.

Locating lightning strikes
It will augment coverage provided by a geostationary satellite, known as GOES-16, that was successfully launched in November 2016. “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, it is possible to give people about the possibility of associated severe weather events like tornadoes and hail.

Experts hope to locate about 90% 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.

Researchers have also discovered different and strange iterations of lightning. For example, so-called dark lightning, powerful bursts of gamma rays, 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.

Biggest riddle
Other surprising and mysterious sorts of lightning are elves and sprites — colourful 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,” Joseph Dwyer, a professor of gamma ray astronomy at the University of New Hampshire, said.

The current thinking is that ice particles in different forms within thunderstorms bump up against one another during updraughts and transfer charges. 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,” Joseph said. “So how does lightning get started inside thunderstorms? It’s one of the biggest mysteries in the atmospheric sciences.”

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