NASA - National Aeronautics and Space Administration

For more information contact:

Rob Gutro
Goddard Space Flight Center, Greenbelt, Md. January 14, 2003
Phone: 301/286-4044

Bruce Buckingham
NASA Kennedy Space Center
Phone: 321/861-7642

Lori Stiles
University of Arizona
Phone: 520/626-4402

Lightning and Lightning Safety

The National Severe Storms Laboratory on Lightning

Global Hydrology and Climate Center (GHCC) Lightning Team

Caption for Image 1: INITIAL LEADER FORKS AND STRIKES THE GROUND IN TWO PLACES

Within Valine and Krider's study sample of 386 flashes, 136 flashes (35%) struck the ground in two or more places that were separated by tens of meters (yards) or more, such as the strike pictured here. The 386 flashes produced a total of 558 different strike points; therefore, on average, each cloud-to-ground flash struck the ground in 1.45 places.CREDIT: Photograph by M. Garay

Caption for Image 2: 1 FLASH, 3 GROUND CONTACTS

These stills taken from a video show one lightning flash striking in three separate places, as indicated in the smaller frames to the left, when the video was slowed. CREDIT: Video photos by N. Parker

Caption for Image 3: LIGHTNING FATALITIES, INJURIES, DAMAGES BY STATE

This is a map of lightning casualties across the contiguous United States between 1959 and 1994. The map was created by the National Weather Service from lightning reports on fatalities, injuries and damages across the United States over that time period. Florida stands out as the state with the most fatalities at 1,523 over the 35 year period. Pennsylvania, North Carolina, New York and Texas are the states with the next largest numbers of fatalities. Alaska and Hawaii reported no lightning-related deaths over that period. CREDIT: National Weather Service

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January 14, 2003 - (date of web publication)

LIGHTNING REALLY DOES STRIKE MORE THAN TWICE

	Image 1

NASA-funded scientists have recently learned that cloud-to-ground lightning frequently strikes the ground in two or more places and that the chances of being struck are about 45 percent higher than what people commonly assume.

Recently, William C. Valine and E. Philip Krider in the Institute of Atmospheric Physics at the University of Arizona, co-authors of the study, took to the field using video and other technology to study lightning, which is one of the biggest weather-related killers in the United States, superseded only by extreme heat and flooding.

They recorded 386 cloud-to-ground (CG) lightning flashes on videotape during the summer of 1997 in Tucson, Arizona. They found that within their sample of 386 flashes, 136 flashes (35 percent) struck the ground in two or more places that were separated by tens of meters (yards) or more. There were a total of 558 different strike points; therefore, on average, each cloud-to-ground flash struck the ground in 1.45 places.

	Image 2

"Most people assume that lightning strikes in only one place. In this research, we've documented that lightning definitely strikes more than one place about a third of the time," Krider said. "If you want to quantify the chances of being struck by lightning, they are about 45 percent higher than the number of flashes because, on average, there are about 1.45 strike points per CG flash."

Within that group of 136 flashes, termed "multiple channel flashes," 88 had two or more separate and distinct channels (or paths) between the cloud base and the ground. Thirty-seven of the flashes forked below the cloud base and struck ground in two or more places. Eleven flashes exhibited both types of behavior. In other words, during the observations in Arizona, for every fork below the cloud there were approximately twice as many flashes that had separate and distinct paths, a ratio that is consistent with previous measurements in Florida.

	Image 3

Valine and Krider also confirmed that after an initial stroke, 67 percent of the new strike points were produced by the second stroke in the flash, rather than the third or fourth stroke. In other words, if any subsequent stroke is going to strike a place different from the first stroke, it is usually the second stroke that does so. The third and fourth strokes usually follow the same path as the second stroke.

Lightning occurs when there is a discharge of electricity between large volumes of excess positive and negative charge that accumulate in thunder clouds. Lightning most commonly occurs in thunderstorms, but it also can occur in snowstorms, sandstorms, in the ejected material over volcanoes. Most lightning takes place within or between clouds; on average, only about one-third of all discharges actually strike the ground. The peak temperature in a lightning channel is around 60,000 degrees Fahrenheit, or about 5 times hotter than the surface of the Sun.

According to the National Weather Service, lightning causes an average of 93 deaths and 300 injuries in the United States each year. The National Severe Storms Laboratory recommends that a safe distance from a previous flash is at least 10 to 13 km (6 to 8 miles) as opposed to the 3 to 5 km (2-3 miles) that experts had previously advised.

The article appears in the latest print issue of the American Geophysical Union's Journal of Geophysical Research - Atmospheres, and publication of the results was funded entirely by NASA.

Lightning Fatalities, Injuries and Damage By State 1959-1994 (Source: National Weather Service)

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