Key to Lightning Deaths: Location, Location, Location
By John Roach
for National Geographic News
|June 23, 2004|
View a map gallery showing the global distribution of lightning flash density. GO >>
Do you know what to do when lightning is near? Read these flash facts
Lightning is a killer. It claims more victims each year than do snowstorms, hurricanes, and tornadoes. It keeps a low profile as the second largest weather-related killer, usually striking one person at a time. Only floods, which can wipe out towns, kill more people.
According to the U.S. National Weather Service, 73 people die from lightning strikes each year and hundreds more suffer life-debilitating injuries. Memory loss, attention deficits, sleep disorders, numbness, dizziness, and weakness are some of the maladies cited.
The highest death rates from lightning in the United States are in Florida, which is known as the lightning capital of the country. According to the service, from 1959 to 2003 lightning killed 3,696 people in the United States. Of those, 425 were in the Sunshine State. (The only state that did not record a lightning death in the period was Alaska).
Lightning has injured at least 2,000 people in Florida since 1959.
"A lot of people in Florida are involved with outdoor activities. People are out golfing, they are out boating, so the odds of getting hit by a lightning flash are greater," said Stephen Hodanish, a senior meteorologist and lightning expert with the National Weather Service in Pueblo, Colorado.
While Florida is also the state where the most lightning flashes strike the ground, injury and fatality rates do not exactly correlate with where the most strikes occur. Rather, lightning tends to strike people in places where there are people to strike.
For example, Colorado is 24th in lightning flash density, but is ranked 10th for lightning casualty rates, said Hodanish. The reason for the discrepancy is that a lot of Coloradoans participate in outdoor activities like hiking and camping in the exposed, lightning-prone high country.
On any given afternoon, unstable breezes and moisture ratchet up cumulonimbus clouds in a whirlwind of updrafts and downdrafts that cause particles of rain, ice, and snow to collide.
The collisions prompt electrical charges to separate. Positive charges shoot high, while negative charges hang low. Electrical imbalance intensifies within the cloud and between the cloud and ground.
"Mother Nature doesn't like to see that," said Hodanish.
In an attempt to restore balance, to equalize the charge separation, lightning flashes rip through the clouds, snap out of the sky, and crack to the ground. The average flash packs enough energy to keep a 100-watt light bulb lit for three months.
The flash of light heats the air around it to nearly 50,000 degrees Fahrenheit (27,760 degrees Celsius), which is hotter than the surface of the sun. The scorching heat forces the air to expand in an explosion of thunder.
The most common form of lightning is intracloud lightning, where negative charges seek a connection with positive charges within the clouds. The flashes stay within the clouds, never making contact with the ground.
The lightning that strikes people is a cloud-to-ground flash. This occurs when the charge imbalance between the cloud and ground becomes so great that the negative charge in the lower part of the cloud begins to travel towards the Earth's surface.
As the charge nears the ground, positive charges surge up tall objects like trees, houses, telephone poles, and, sometimes, people. When the negative charge from the cloud connects with these positive charges rising from the ground, a bright flash occurs.
The flashes that reach the ground splinter trees, char forests, and kill people. Cost estimates of the damage caused by cloud-to-ground lightning total in the hundreds of millions of dollars each year, according to the National Weather Service.
Where Lightning Strikes
Thunderbolts rain down with the greatest fervor on tropical, central Africa, according to an analysis of satellite data by a team of researchers with the National Aeronautics and Space Administration's Global Hydrology and Climate Center in Huntsville, Alabama.
The weather patterns in Africa bring in warm air from the Atlantic Ocean which collides with mountains, producing thunderstorms year-round.
Another lightning hotspot is the Himalayas, where the mountainous topography forces the convergence of air masses from the Indian Ocean. The North and South Poles, however, rarely experience thunderstorms and, therefore, have almost no lightning.
In the United States, lightning researchers estimate that 22 million lightning flashes strike the ground each year. The most lightning prone region is Florida, which has, on average, 12 flashes of lighting per square kilometer per year.
"To produce lightning you need thunderclouds. To produce thunderclouds you generally need heat and moisture and both are plentiful in Florida," said Vladimir Rakov, an electrical engineer and lightning expert at the University of Florida in Gainesville.
The Florida peninsula is sandwiched between the Gulf of Mexico and the Atlantic Ocean. Sea breezes from both sides move inland as the day progresses, colliding over the warm landmass, explained Hodanish.
"If it wasn't for the sea breezes colliding with each other, the lightning activity would be significantly less," he said. Such is the case, he added, with southeastern Texas, which has similar weather to Florida, but just one coast.
Throughout the United States, lightning frequency generally decreases from the southeast to the northwest. Pockets of intensity include the Rocky Mountains, where the topography causes thunderstorms to form with regularity in the summer months.
Summertime is when most lightning occurs in the United States, but it can also strike during the winter months in a rare thunder snowstorm.
As for the question as to whether or not lightning can strike the same place twice, Rakov says that the answer depends on what kind of place that is.
Statistically, he said, during cloud-to-ground lightning, the channel of discharge is merely looking for a place on the ground, which is a random act assuming the ground is flat and geologically uniform.
For example, Rakov says that one square meter of terrain in a flat Florida field gets hit by lightning once every 100 millennia, thus if that area gets hit, it would not be hit for another 1,000 human generations, which he considers in all practical purposes to be never.
The reality, however, is that the ground is not uniform and lightning is attracted to certain ground features and not to others. "From a lightning point of view, yes, it does strike the same place many times, particularly if it is a tall structure," said Rakov.
Hodanish said studies have shown that tall structures such as New York's Empire State Building get struck several times in a single storm. "Typically the tallest objects get hit the most frequently," he said.
To avoid death by a flash of lightning, the National Weather Service recommends following the "30/30" rule. When lightning is seen count the time until thunder is heard. If it is 30 seconds or less, seek shelter immediately and stay there for at least 30 minutes after the last rumble of thunder is heard.
"Typically, people go out and resume activity too quickly and end up getting hit," said Hodanish.
Covered picnic shelters, tents, and convertibles even with the roof up are not safe. Rakov said that shelter should be a substantial building such as a home or inside a car with a metal roof.
"If neither are available, make yourself as small a target as possible," he said. "Never stand near tall trees, metal fences, or water." Metal objects are popular targets of lightning and power lines can conduct lightning surges over large distances, he added.
According to Hodanish, who is working on a scientific paper about a man who was struck and killed by the first lightning flash of a storm on top of Colorado's Pikes Peak, "for some, no matter what precautions you take, you can be the unfortunate victim of lightning."
For more news on lightning, scroll down
|© 1996-2008 National Geographic Society. All rights reserved.|