Scientists are becoming increasingly convinced that a rapid increase in inter-cloud lightning—lightning that occurs between clouds without hitting the ground—is a strong indicator of severe weather. Image: Flickr/Lauri Väin
An unassuming-looking rod on a rooftop in Beltsville, Md., connected with wires to specialized computer equipment in the building below, is helping scientists pinpoint the location of lightning as it flashes during a thunderstorm. Working in tandem with nine other identical devices installed throughout the Washington, D.C., area, these sensors promise to help usher in a new era of severe weather prediction.
Called the Washington D.C. Lightning Mapping Array (DC LMA), the devices detect, in real time, high-frequency radio waves emitted by lightning in the surrounding region.
Scientists are becoming increasingly convinced that a rapid increase in inter-cloud lightning -- lightning that occurs between clouds without hitting the ground -- is a strong indicator of severe weather. These increases have been shown to occur about 20 minutes before the event, while the current average lead warning time for tornadoes is 13 minutes (ClimateWire, May 31).
By 2015, new satellites circling the Earth's equator will be responsible for detecting these lightning jumps, giving meteorologists across the nation greater confidence when predicting tornadoes and other severe weather events. The DC LMA is now being used to train meteorologists to interpret this new data.
"We're using these ground-based observations to prepare forecasters so they can use the satellites as soon as they're in orbit," said National Oceanic and Atmospheric Administration researcher Scott Rudlosky, who helps run the array.
"Because we're trying to mitigate that gap, we want to have all the different operational users ready to go as soon as that satellite's turned on," he said.
Mapping dangerous strikes
U.S. government agencies NASA, NOAA and the New Mexico Institute of Mining and Technology sponsor the lightning array, and colleges and universities throughout the D.C. metropolitan area host the stations. The array started running in 2007 and can detect a lightning storm as far as 120 miles away from its center.
As lightning emits radio waves, these waves hit the DC LMA's rods at different times. Computers are then able to triangulate exactly where and when the lightning occurred and transmit these data instantaneously.
When multiple storms are happening at once, seeing upticks in lightning frequency can help forecasters increase their confidence of severe weather warnings.
"When you have multiple storms going on at the same time, the forecaster really has limited time to get out the warnings," Rudlosky said. "What this data really provides the ability to do is identify which storms should we be focusing on at this instant."
The DC LMA is incredibly precise. Last week, a lightning strike in Annapolis, Md., left two men badly injured. After the fact, Rudlosky was able to use DC LMA data create a 3-D image of the lightning strike that was likely responsible.
"Within a fraction of a second, we can tell when that lightning flash occurred," Rudlosky said.
Another goal driving the research is to "better inform the public and keep them as safe from lightning as much as we can," he added. "These lightning mapping arrays have actually changed the criteria for how long before or how far away the lightning needs to be before you should be worried."
New satellites aim to provide instant lightning data nationwide
There are now seven LMA networks in the United States, including arrays in tornado-heavy areas like north Alabama, Oklahoma City, Colorado and west Texas. But it would be too expensive to deploy technology like the DC LMA across the country -- Rudlosky estimates that a similar array would cost about $300,000 today.