Southern AERA Quarterly Activity Bulletin of The South Carolina Department of Natural Resources-Southeast Regional Climate Center
Volume 4, No. 4
Every year, lightning strikes the ground around 40 million times in the United States. Lightning causes many injuries and fatalities each year. Lightning research has come a long way, but many questions still remain. Pay close attention to the information that follows to learn what lightning is and why it occurs. It is important to understand the nature of this weather phenomenon so that precautions may be taken to avoid injury or even death.
Lightning is a flash of electricity that strikes within and between clouds, from clouds to clear air, and from clouds to the ground. The type of lightning that is most threatening to us is cloud-to-ground lightning, as that is the kind that causes damage to people and the things that they value.
Lightning occurs because positive and negative charges are attracted to one another. Negatively charged particles will try to move toward positively charged particles. When these particles of opposite electrical charge connect, lightning occurs.
Scientists are still trying to discover exactly how positive and negative
charges build in different parts of clouds and the areas surrounding the clouds.
One explanation is that negative and positive charges are left on different
sized raindrops as they collide within the cloud, and then the larger raindrops
bring a negative charge down to the bottom of the cloud while the smaller
particles gain a positive charge and settle at the top of the cloud. Another
explanation is that updrafts, or upward-moving air currents found inside
thunderstorms, carry positive charges normally found near the ground upward,
while downdrafts, or downward-moving air currents found inside thunderstorms,
carry negative charges from the upper air downward. Many scientists believe that
a combination of the two theories is a more accurate explanation.
Take a look at the lightning diagram for an explanation of a cloud-to-ground lightning strike.
Lightning is a massive electrical discharge that explodes when charges within a thunderstorm become strong enough to cause electricity to flow through air, which is not a very conductive substance. Conductivity refers to the ability of a substance to carry electricity. Since air is a weak electricity conductor, the charges built up around a thunderstorm must be very strong to pass electricity. Lightning often strikes tall objects that stand alone. This is why trees are a typical target for lightning. Since the stepped leader has to travel down from the cloud, it will seek out the shortest traveling distance to reach the ground.
Every lightning flash produces thunder. Thunder occurs because of the rapid heating of the air around a lightning flash. The heating is so intense and sudden, that the air molecules near a lightning flash explode and create the sound waves we hear as thunder. Since sound waves travel more slowly than light waves, we always see the lightning flash before we hear the sound of the thunder it makes. This fact makes it easy for us to tell just how far away the lightning flash is. In order to do this, just count the number of seconds between the time you spot the lightning flash and the time you hear the thunder, and divide by five. This is useful information, as you can keep track of your calculations and determine if the thunderstorm is getting closer or further away. If it is coming closer, take cover!
Each year, about 100 people in the United States are killed by lightning, and several hundred people are injured. It is very important to realize what a powerful force lightning is, and take all of the necessary precautions to avoid any lightning mishaps. The best way to protect yourself is to stay indoors during thunderstorms. Do not talk on the phone during storms either, as many people have been killed this way. Stay away from metal objects like faucets, wires, and pipes, as metal is a very good conductor of electricity and may attract lightning if it should happen to hit your house. Stay away from metal objects when outside of your house especially. A fence or railroad track is a dangerous thing to be near during lightning. If other shelter is not available, get into a car that has a metal roof. If lightning strikes the car, the metal on the car will pass the electricity safely to the ground without harming you. Since lightning seeks the shortest traveling distance to the ground, keep away from trees, flagpoles, telephone poles and other objects that stand much taller than their surrounding area. Also keep in mind that if you are in an open field or on a golf course, YOU may be the object standing much taller than the surrounding area, so you should take shelter quick! Do not swim during thunderstorms, and stay away from pools and lakes. Since water is a good conductor of electricity, it is dangerous. If you cannot find any kind of shelter, crouch on the ground with your head down and only your feet touching the ground; do not lie down as lightning may travel on the wet ground and shock you.
1. How many people were injured by lightning in North Carolina between 1959 and 1997?
2. What was the second leading cause of lightning-related casualties in North Carolina between 1959 and 1997?
3. How many more total lightening injuries occurred than total fatalities in North Carolina?
4. Why do you think golfing is a high risk activity during a lightening storm? What makes it more dangerous than other outdoor sports?
5. Where do you think "various/other locations" refer to? What are other high risk activities during lightening storms?
6. What are some "water related" activities that could result in injury/death during a lightening storm?
7. Based on what you just read about lightning, what should these people have
done to increase their chances of survival?
8. How many people were killed by lightning while standing under trees (look very closely)?
9. How many people were killed while talking on the telephone?
10. How many fatalities could have been prevented by following the lightning safety tips you just read?
11. What do you call the flow of negatively charged particles that comes down from the cloud toward the positively charged particles near the ground?
12. What does the term conductivity refer to?
13. What type of lightning is the most dangerous to people? Why?
14. What are updrafts? What are downdrafts?
15. Why does thunder occur?
16. If you watched lightning flash in the distance and counted 25 seconds before you heard the thunder, how far away was the lightning? How do you know this?
17. Why is it dangerous to go swimming when a thunderstorm is near?
18. Why do you think it is especially dangerous to go golfing when a thunderstorm is near other than the fact that you are standing in an open space?
19. Which travel more quickly, sound waves or light waves?
20. About how many people are killed each year by lightning in the United States?
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Southern AER is a quarterly publication of the Southeast Regional Climate Center. Funding is provided by a grant from the National Oceanic and Atmospheric Administration.
Internet Resources On Lightning