' Enlightening ' Facts And Safety Tips About Lightning

Average Lightning Stroke is 6 miles long.

The Temperature of lightning's return stroke can reach 50,000 degrees Fahrenheit. The surface of the sun is not even that hot! (around 11,000 degrees Fahrenheit).

Average Thunderstorm is 6-10 miles wide.

Average Thunderstorm travels at a rate of 25 miles per hour.

Once the leading edge of a thunderstorm approaches to within 10 miles, you are at immediate risk due to the possibility of lightning strokes coming from overhanging anvil cloud. Because of this, many lightning deaths and injuries occur with clear skies directly overhead.

On average, thunder can only be heard over a distance of 3-4 miles, depending on humidity, terrain and other factors.

Approximately 100,000 thunderstorms occur in the United States each year. Approximately 10% of all thunderstorms are severe enough to produce high winds, flash floods, and tornadoes.

Thunderstorms cause an average of 200 deaths and 700 injuries in the United States each year.

These facts are taken from the Automated Weather Source Online

Lightning Safety Rules courtesy of the
National Oceanic and Atmospheric Administration (NOAA)
U. S. Department of Commerce

Stay indoors, and don't venture outside, unless absolutely necessary.

Stay away from open doors and windows, fireplaces, radiators, stoves, metal pipes, sinks, and plug-in electrical appliances.

Don't use plug-in electrical equipment like hair dryers, electric toothbrushes, or electric razors during the storm.

Don't use the telephone during the storm. Lightning may strike telephone lines outside.

Don't take laundry off the clothesline.

Don't work on fences, telephone or power lines, pipelines, or structural steel fabrication.

Don't use metal objects like fishing rods and golf clubs. Golfers wearing cleated shoes are particularly good lightning rods.

Don't handle flammable materials in open containers.

Stop tractor work, especially when the tractor is pulling metal equipment, and dismount. Tractors and other implements in metallic contact with the ground are often struck by lightning.

Get out of the water and off small boats.

Stay in your automobile if you are traveling. Automobiles offer excellent lightning protection.

Seek shelter in buildings. If no buildings are available, your best protection is a cave, ditch, canyon, or under head-high clumps of trees in open forest glades.

When there is no shelter, avoid the highest object in the area. If only isolated trees are nearby, your best protection is to crouch in the open, keeping twice as far away from isolated trees as the trees are high.

Avoid hilltops, open spaces, wire fences, metal clotheslines, exposed sheds, and any electrically conductive elevated objects.

When you feel the electrical charge -- if your hair stands on end or your skin tingles -- lightning may be about to strike you. Drop to the ground immediately.

The idea of preventing a lightning strike goes back to 1754 when the master himself, Ben Franklin, was still experimenting. Prokop Divisch installed 216 earthed points on a 7.4 meter wooden frame and a few years later it was suggested by Lichtenberg that a catenary of barbed wire over a house could prevent a strike. The idea of using multiple points to discharging a cloud and neutralize its charge has been thought of for years and even tried. Recently however, many people have claimed success. First they claimed to discharge the cloud and when that was proven impossible, they claimed to prevent a strike from occurring. Various branches of the U.S. government have tested several different types over the years without success of any kind. One 1975 report was done by the Office of Naval Research, NASA, FM, and US Air Force. A 1,200 foot tower at Eglin AFB, which was fitted with a multipoint system, sustained eleven hits in three months. Five were photographically recorded while seven other strikes were monitored, using NASA's magnetic links, as having had strikes in the 30 to 48kA range. The report also has a picture of a video monitor showing NASA's 500 foot meteorological tower at Kennedy Space Center being hit. It too had a multipoint array. In the report, R. H. Golde suggested an umbrella shaped barbed wire device could be used on very tall towers to prevent the normally occurring streamers.

As the height of an object is increased, the number of strikes increases. This was proven in the middle of this century with testing at the Empire State Building. Most of the strikes to this structure were caused by upward streamers triggering the strike. Golde's concept is to meticulously form a uniform field shaped element which takes into account the electrostatic effects of surrounding points. If all points are positions with the correct outward looking angle, it could spread the E field out much like a corona preventor on a high voltage power supply. Since it is made of discharge points, unlike the rounded corona preventor, the electrostatically inducted voltage from the tower/ground system will be spread to limit the size of the upward streamer. The effect on the downward approaching stepped leader is nil. As the stepped leader approaches the array of points, the E fields will increase above the ability of the size of the array to prevent the transition from ion-maker to streamer producer (glow to arc transition). This is similar to (but not the same as) reaching the limit of the corona preventor on a high voltage power supply. The air breaks down and a major streamer/arc leaps outward. The larger the array means the larger the support structure. (Ice and wind tower loading also increase.) More charge can now be stored on this structure before the array can bleed it off into the wind. This can result in larger streamers from the array as E fields increase with the approach of the stepped leader.

A more recent test of various types of multipoint arrays was done in the late 1 980's by the FM (terminated on 1/11/90). The FM report also concludes that the tower arrays under test were struck and damaged. The report further includes photos of the video tape of the strike and the NASA magnetic links current measurement for one strike was 8kA for one down conductor and 10kA for the other. Other damage to the facility was listed together with eyewitness accounts.

The many claims from the array suppliers are as different as the clouds. Few suppliers will agree whether it prevents a strike 1QQ% or just minimizes the chances of a strike. Another is whether to ground the array or not and how important the ground is to the functioning of the arrays.

Some of the arrays on the market consist of small rounded brushes which when hit, splatter molten metal as far away as 10 meters. This can be a fire hazard. The FAA report quotes the eyewitnesses to the August 27, 1989 strike to the Tampa ATC Tower: "sparks like the slag you get when arc welding."

Mother Nature produces a large variation of strikes. The larger strikes will have larger E fields and the stepped leaders will be longer. This means the larger strikes will overwhelm the array and upward streamers will reach out and grab the stepped leader anyway. The solution for lightning protection is for you to have control of the strike energy and not Mother Nature. To do this, a well-designed ground system will be a better investment than cluttering up the top of your tower.

NASA Records Color Storm Flashes In Space

Spectacular red and blue flashes of light extending upward from electrical thunderstorms to altitudes as high as 60 miles were recorded by NASA researchers utilizing special low-level, all-sky cameras aboard jet aircraft.

According to Principal Investigators Davis Sentman and Eugene Wescott, professors at the Geophysical Institute with the University of Alaska at Fairbanks, the unusual flashes occurred over thunderstorms in the Midwest between June 28 and July 12,1994.

"The flashes look like the Fourth of July...like Roman candles with fountains," said Sentman. "Some of the flashes extend up through the ozone layer into the base of the ionosphere, the region of the upper atmosphere where auroras occur."

Sentman and Wescott captured 19 black-and-white images of flashes above thunderstorms in the Midwest last year. One flash was recorded for about every 300 cloud-to-ground lightning strikes during the flights sponsored by NASA's Space Physics Division.

In replicating the study this summer, the researchers were able to accurately measure the position and altitude of the flashes and to examine their color and speed. They also identified two distinctly different flashes, which they named sprites and blue jets.

Sprites are blood red flashes that appear with bluish tendrils dangling from the bottom of some. The flashes, which last only a few thousandths of a second, extend from above storm clouds up to about 60 miles high, reaching the bottom of the ionosphere. Recorded radio noise coincided with the sprite flashes. When the recorded signals are played through a speaker, they "pop," a sound that differs from normal lightning discharge signals.

The sprites were recorded on a TV spectrograph and will be analyzed to determine their atomic and molecular source. Since they are associated with thunderstorms and lightning, scientists suspect the flashes may be a form of electrical discharge. If so, they could present a concern to high-altitude research aircraft and could be responsible for creating a host of chemical reactions in the upper atmosphere, including modifications of upper atmosphere ozone.

Blue jets are flashes that appear in narrow beams, sprays, fans or cones of light which give off a blue or purple hue. "To the eye, they resemble material ejected from a high explosive source, the tracks of atomic particles, or rays in a cloud chamber," Westcott said.

Observed over a thunderstorm in the Midwest, the top of the sprite is higher than 280,000 feet. The root-like tendrils are as low as 195,000 feet. Beneath the sprite is an overexposure of lightning occurring at the thunderstorm's cloud top which is 55,000 feet high.

A family of sprites is captured by using triangulation of the images of the same sprites taken from two aircraft. The thunderstorm's cloud top is at an altitude of about 42,000 feet and the highest parts of the sprites occur at an altitude of 59 miles.

Large blue jets shooting upwards from a thunderstorm's top can reach an upper altitude of about 130,000 feet. Blue jets appear to move at speeds of 45,000 to 223,000 miles per hour which is well above the speed of sound but far below that of light or radio waves.

Pilots and others have reported seeing blue or green columns of light above thunderstorms for years, but Sentman and Wescott were the first to capture them on video. Blue jets appear to originate at the top of storm clouds and then travel upward to an altitude of about 20 miles. They occur at various angles with speeds ranging from 20 to 60 miles a second.

Return to the top of this page