Lightning strikes

Factors involved: Chemical reactions, rain, temperature, weather conditions

Regions affected: Cities, coasts, forests, lakes, mountains, plains, towns, valleys

Definition

Strikes of lightning fatally wound between fifty and one hundred persons each year in the United States, mostly within the thunderstorm season that occurs during the spring and summer months. Lightning also causes tens of millions of dollars of damage each year by sparking large forest fires and destroying buildings and various forms of electrical and communication systems.

Science

A lightning bolt is a high-voltage electrical spark which occurs most often when a cloud attempts to balance the differences between positive and negative charges within itself. Lightning bolts can also be generated between two clouds, or between a cloud and the ground, although these conditions occur much less often. A lightning bolt is generally composed of a series of flashes, with an average of four flashes. The length and duration of each flash will vary greatly.

Thunder is caused by the heating of air surrounding a lightning bolt to temperatures as high as 72,032 degrees Fahrenheit (40,000 degrees Celsius), which is approximately five times hotter than the sun, causing a very rapid expansion of air. This heated air then moves at supersonic speeds under a force ten to one hundred times normal atmospheric pressure, thus forming shock waves that travel out from the lightning at speeds of approximately 1,083 feet (330 meters) per second.

Thunderstorms are local rainstorms that feature lightning and resultant thunder claps; they sometimes produce hailstones. Much less often, lightning is created by snowstorms, dust storms, or clouds produced by volcanic eruptions or thermonuclear explosions. The explosive release of electrical energy within a thunderstorm cloud creates a lightning bolt, which is most often produced by accumulations of electrical charge within the same cumulonimbus cloud. Cloud-to-cloud lightning involves one cloud which is seeking an oppositely charged cloud to neutralize itself. Cloud-to-ground lightning involves a lightning bolt which is seeking the best conducting route to the ground, thus hitting lightning rods, tall buildings, and trees.

Thunderstorms occur when the atmosphere is unstable and moist air at the ground surface rises, creating several small cumulus clouds that initially dissipate while producing rain or electrical charges. As the clouds increase in size and combine, they surge upward and generate rain and lightning. The average storm produces five to ten flashes per minute, whereas larger clouds can produce electrical discharges of over a thousand flashes per minute. A single thunderstorm cloud has the potential to build up an electrical charge of approximately 1 million volts per meter, produced by the action of the rising and falling of air currents. This electrical charge is transferred through the cloud as raindrops, hailstones, and ice pellets collide with smaller water droplets and possibly ice. A falling stream of electrons creates a negative charge, which generally accumulates in the lower part of the cloud, with the positive electrons simultaneously creating a positive charge in the upper part of the cloud. Lightning is essentially the reaction that neutralizes these positive and negative charges.

Other functions of lightning are to enhance rain and snow formation, supply energy to tornadoes, and assist in the fixation of atmospheric nitrogen. Other forms of lightning include ball lightning, also called kugelblitz, a rare phenomenon in which round balls of fire appear, often near telephone lines or buildings. Heat lightning involves lightning seen from a distant thunderstorm which is too far away for the thunder to be heard.

American scientist Benjamin Franklin performed the first systematic study of lightning in the late eighteenth century, working from his hypothesis that sparks observed in his laboratory experiments and lightning were both forms of the same type of electrical energy. During a Pennsylvania thunderstorm in 1752, he flew the most famous kite in history, with sparks jumping from a key tied to the bottom of the damp kite string to an insulating silk ribbon tied to Franklin's knuckles. The kite took the place of a lightning rod, and Franklin's grounded body provided the conducting path for electrical currents originating from the storm clouds. Franklin's experiments proved that lightning strikes do contain electricity and determined that the lower parts of the clouds were negatively charged, with Earth providing the positive charge. Franklin's research also laid the groundwork for the implementation of lightning rods as a means of protecting buildings.

Geography

An estimated fifteen hundred to two thousand thunderstorms occur somewhere on the Earth's surface at any given moment. These thunderstorms are estimated to trigger approximately one hundred or more lightning flashes every second, which corresponds to approximately 8.6 million strikes every day and more than 3 billion every year. Lightning has also been known to occur within atmospheric storms on other planets within Earth's solar system, such as Jupiter and Venus.

Lightning occurs most commonly in warm and moist climates. In the United States, the hot and humid climate of Central Florida experiences the highest occurrence of lightning strikes and the Pacific Northwest sees the lowest occurrence.

Prevention and Preparations

The National Lightning Detection Network was set up in the 1970s to assist meteorologists in locating and tracking thunderstorms and lightning strikes. This intricate computer network utilizes lightning detection images from orbiting satellites and other equipment which reveal precisely where severe storm activity is located, in addition to the exact locations where lightning has occurred and has possibly hit the ground.

Thunder is an important warning signal by nature which reveals that a lightning bolt has just fired within approximately a 10-mile radius. The commonly used "flash-to-bang" method is effective in estimating how far away this most dangerous part of a storm is occurring. Once a flash of lightning is visibly observed, the number of seconds until thunder is heard is counted. The speed of light is 186,300 miles per second, thus enabling lightning to be seen immediately after it flashes. By contrast, sound waves travel about a million times slower at approximately one mile every five seconds. To estimate the approximate distance from the location of an individual to the lightning strike, one should divide the number of seconds between the "flash" and the "bang" by five to obtain the distance away that the lightning occurred in miles. If the lightning and thunder are extremely close together, one should divide the difference between the lightning and thunder by 360 to obtain the estimated distance away that the lightning occurred in yards.

Common sense dictates that an individual caught near a thunderstorm should seek safe shelter immediately, particularly if the "flash-to-bang" time is only ten to fifteen seconds, as this means that the lightning is only 2 to 3 miles away. Successive lightning strikes within the same storm can be used to determine if the thunderstorm is approaching one's location or moving away. If the time interval between the lightning and the thunder is getting progressively shorter, the storm is getting closer. If time between the lightning and the thunder is getting progressively longer, the storm is moving away from one's location.

The best defense against getting struck by lightning is prevention, in the form of examining the weather forecast before participating in any outdoor activities. Continually being on the lookout for clouds that appear to be forming into thunderstorms is critical, as is heading for shelter at the first sight of lightning or the first sound of thunder. The occurrence of thunder means that lightning must be present somewhere even if it is not directly visible, with the flash often hidden within thick clouds.

The best shelter from lightning is a large, permanently fixed, and electrically conductive building, staying away from windows and other breakable objects. Sheds and small buildings, particularly those constructed with wood and masonry and that do not contain a lightning rod, do not provide nearly as much protection. In the event that a building is not available, taking refuge in a motor vehicle with a metal roof can provide some protection, as the lightning current has a chance to pass harmlessly down through the vehicle and dissipate into the ground. Regardless of the structure in which a person seeks cover, it is important to refrain from touching any metal surfaces. Locations that contain flammable fuels, such as gasoline, should be avoided during a thunderstorm.

Persons are advised to avoid being exposed in open areas, high places, or near isolated trees during lightning danger periods. Those caught in the water during a storm, such as while swimming, have a much greater chance of experiencing electrical shocks in the event that lightning strikes an area nearby. Saltwater, a better conductor of electricity, is less dangerous than freshwater as the electrical current tends to flow around, rather than through, an individual or boat in the water.

Lightning rods are important protection devices required to be placed within all modern structures. They are made from metal strips that conduct lightning discharges through the building and into the ground. Arresters are often used in locations where power, telephone, and antenna wires enter buildings. Ground wires involve cables that are strung above other wires in an electrical transmission line, in the hope that they will become the preferred target for a lightning surge.

Rescue and Relief Efforts

The heavy currents of large lightning bolts have been known to shatter masonry and timber, and they often start fires. Lightning has been documented injuring critically or even killing persons talking on corded telephones, taking a bath, or sitting near electrical units such as a computer. Cadaver studies on victims of fatal lightning strikes reveal that death can occur from heart damage, inflated lungs, brain damage, and burns.

For those who survive a lightning strike, immediate medical attention is necessary. If the victim is not breathing, artificial respiration can provide adequate short-term life support, though the victim may become stiff or rigid in reaction to the shock. Survivors of electric shock, from lightning or other sources, may suffer from severe burns and permanent aftereffects, including cataracts, angina, or nervous-system disorders. Amnesia and paralysis can also occur.

Impact and Research

Science has confirmed that lightning is one of the strongest forces in nature, with larger bolts generating an average potential difference of 100 million volts of energy, approximately equivalent to the power contained in a middle-sized nuclear reactor.

Data collected by the National Weather Service reveal that lightning strikes kill an average of forty-five people each year in the United States and injure hundreds more, mostly during the spring and summer months. Fatalities can occur from direct hits, so-called side flashes (in which a nearby object is directly struck and some of the energy short circuits into the victim), conduction through other materials, and ground current.

Lightning is also to blame for over 10,000 forest fires each year in the United States alone, with the total property replacement cost in the tens of millions of dollars. Lightning research greatly increased in the 1960s, motivated by the danger of lightning to both aerospace vehicles and the solid-state electronics used in computers and other technical devices. Commercial airliners performing a normal number of service runs are subjected to an average of one lightning strike per year, and in many cases the lightning is triggered by the airplane itself.

Historical Overview

Lightning, or "thunderbolts," have long been feared and revered by societies with beliefs in the supernatural, such as the Greeks, Vikings, Buddhists, and Native Americans. Thunderstorms occur throughout the globe, even in Africa's Sahara Desert, and many societies have produced myths that associate lightning, a frightening and long-misunderstood phenomenon, with supernatural power. Lightning predicted a victory by Gilgamesh, Sumerian hero of an epic dating to the third millennium BCE. Zeus, chief god of the Greeks, hurled thunderbolts, and Thor, the thunderer, was the strongest of the Norse gods. Thunder and lightning on Mount Sinai preceded presentation of the Ten Commandments to Moses. The Romans considered the location of lightning to be an omen favoring or discouraging personal and governmental business. Many cultures believed that objects struck by lightning held magical powers, but people's primary concern has been protection from the unpredictability of lightning, with its associated fire and destruction. Romans wore laurel leaves for protection, and, in the Middle Ages, European fire festivals sought protection for communities.

Simultaneously, rational explanations for lightning have encountered superstition. Greek philosopher Socrates described a storm as "a vortex of air." Aristotle theorized that a cooling and condensing cloud forcibly ejects wind which, striking against other clouds, creates thunder. He wrote, "As a rule, the ejected wind burns with a fine and gentle fire, and it is then what we call lightning." Greek historian Herodotus observed that lightning strikes tall objects, and Mongol law recognized the fatal association between lightning and water, forbidding washing of clothes or bathing during thunderstorms. Italian artist and scientist Leonardo da Vinci theorized that clouds forced together by opposing winds could only rise, and he thus connected storm clouds with updrafts.

Not until the eighteenth century was lightning associated with electricity, itself a little-understood phenomenon named in the late 1500s by Elizabethan court physician William Gilbert after the Greek philosopher-scientist Thales of Miletus's experiments with amber, or, in Greek, electra. During the seventeenth and eighteenth centuries, electricity and magnetism attracted experimentation and showmanship. Only when knowledge of European experiments and gifts of apparatus, including glass Leyden jars capable of holding and storing electrical charges, came to American Benjamin Franklin in 1746, did a theory of electricity emerge. Franklin determined that there was a single type of electricity, confirmed speculation that lightning was electricity and, in 1749, first proposed that metal rods could protect buildings and ships from strikes. His suggestions for construction, placement, and grounding appeared in the 1753 Poor Richard's Almanac.

Practical applications of electricity, including American inventor Thomas Alva Edison's 1879 invention of a durable light bulb, and the subsequent problems of distribution along power lines vulnerable to lightning, encouraged lightning research. Despite lightning rods on poles, lightning struck power lines and disrupted service. Solutions required accurate measurements of lightning voltage and speed of discharge, studies led by the companies Westinghouse and General Electric engineers. German immigrant Charles Steinmetz built high-voltage generators to simulate lightning. Generators produced 50-foot bolts of lightning for New York World's Fair visitors in 1939, but laboratory apparatus could not equal the energy of natural lightning.

In 1925, Sweden's Harold Norinder, using the European-developed cathode-ray oscilloscope, measured a lightning-induced electrical surge of about a ten-thousandth of a second, and Americans measured lightning strikes on power-transmission lines of 5 million volts in under two-millionths of a second. Understanding the magnitude of the problem led to improved protection, reducing power failures.

Research leading to recognition of weather conditions likely to produce lightning, and knowledge of the location of lightning strikes serves military, commercial, and public interest and furthers technological advances. Practical applications of scientist Robert H. Goddard's 1929 Massachusetts launch of a rocket carrying a barometer, thermometer, and camera improved both World War II rocket design and television cameras. In 1959, scientists conducted the first meteorological experiment on a satellite platform. On April 1, 1960, the launch of the polar-orbiting Television Infrared Operational Satellite, TIROS-1, inaugurated the era of satellite meteorology. Capability expanded December 6, 1966, with the launch of the first geostationary meteorological satellite. Research begun at the University of Arizona in the 1970s evolved into the US National Lightning Detection Network under Global Atmospherics Incorporated, the product of a 1995 merger, which supplied data to local forecasters.

Lightning has caused more deaths than tornadoes or hurricanes in the United States but far fewer injuries and less property damage. Despite advances in radar and satellite remote sensing and increasing reliability of forecasts, weather predictions warn only of the potential for lightning, and technology locates lightning only as it occurs. Public and private agencies stress public awareness and education in safety procedures to minimize exposure to strikes and fatalities.

Bibliography

Alvarez, Lizette. "Hit By Lightning: Tales From Survivors." The New York Times, 18 July 2017, www.nytimes.com/2017/07/18/us/hit-by-lightning-tales-from-survivors.html. Accessed 31 Jan. 2019.

Dennis, Jerry. It's Raining Frogs and Fishes: Four Seasons of Natural Phenomenon and Oddities of the Sky. New York: HarperCollins, 1992. Very readable manuscript highlighting lightning strikes and other natural phenomena within the atmosphere.

Gardner, Robert L., ed. Lightning Electromagnetics. New York: Hemisphere, 1990. Text applying examples from physics and electronics to the natural events occurring during a thunderstorm.

"Lightning Science: Five Ways Lightning Strikes People." National Weather Service, US National Oceanic and Atmospheric Administration, 2019, www.weather.gov/safety/lightning-struck. Accessed 31 Jan. 2019.

Rakov, Vladimir A., and Martin A. Uman. Lightning: Physics and Effects. New York: Cambridge University Press, 2003. Covers all aspects of lightning, including physics and protection. Accessible to general readers.

Renner, Jeff. Lightning Strikes: Staying Safe Under Stormy Skies. Seattle: Mountaineers Books, 2002. Discusses the risks of lightning, thunderstorm winds, and floods. Offers practical strategies for avoiding lightning.

Salanave, Leon E. Lightning and Its Spectrum: An Atlas of Photographs. Tucson: University of Arizona Press, 1980. Document relating the physics principles behind lightning formation and its spectrum.

Uman, Martin A. The Lightning Discharge. Mineola, N.Y.: Dover, 2001. Excellent description of the intricate process of lightning discharge in various environments.

Williams, Jack. The Weather Book. 2d rev. ed. New York: Vintage Books, 1997. An often-referenced text giving excellent descriptions of various weather patterns such as thunderstorms and catastrophic events such as lightning strikes.