ATMS 120 Lecture Notes - Lecture 3: Lightning, American Meteorological Society, Electric Field

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Published on 9 Jul 2015
School
University of Illinois
Department
Atmospheric Sciences
Course
ATMS 120
Lightning History
Lightning is often regarded as one of the most mysterious and extreme forms of weather, and our goal
in this learning module is to unravel the mysterious nature of this weather phenomenon. Lightning has
perplexed mankind for centuries and up until recently, much about lightning was not understood.
Lightning has played a pivotal role in human existence as it was most likely the vessel that brought
mankind fire. In ancient Greece, lightning was thought to be the weapon of Zeus, the most powerful
Greek god, which was used to protect Greece from its enemies and also to punish the Greeks when
their actions did not please the gods. When Zeus was upset or displeased, he would throw large bolts
of lightning down from his home on Mt. Olympus.
Scientifically, one of the first written accounts of lightning was found in the works of Aristotle (384–322
BC). He explained, incorrectly, that thunder was the result of the frequent and violent collisions
between updrafts and downdrafts within a cloud as they “inhaled and exhaled.” It was not until the
1700s that scientists were able to generate large amounts of electricity in a laboratory setting so as to
create large arcing sparks between two conductors. It was noted numerous times that these large
sparks were associated with a really loud pop or crack, and many drew a similar conclusion between
lightning and thunder. For example, in the video below, listen to the noise made when this electrical
connection is broken.
The most significant milestone in the early history of lightning research occurred in 1752, when
Benjamin Franklin (1706–90) performed his famous kite flight. Although history is unclear if Franklin
performed this experiment himself, the idea was published by Franklin in 1750. Unfortunately, many
who performed this experiment un-insulated fell victim to the electricity. However, Franklin’s work in
electricity led to the invention of the lightning rod and he is credited for assigning the labels “positive”
and “negative” to the different polarity of electricity.
Modern science has made huge leaps and bounds in the physical understanding of the lightning
strike, and our goal is to unpack and understand the latest scientific findings. Before we move on to
Part 2 of this lecture, it is important to see what we already know about lightning. Please take a few
moments to complete theLightning: Myth or Fact? quiz. Good luck!
Lightning Myth or Fact—Answers!
#1. Myth or Fact: Lightning always produces thunder. FACT
All lightning strikes produce thunder, but sometimes the storm is so far away from you that you can't
here the thunder. So, you see the lightning, but don't hear the thunder. This phenomenon has been
called "heat lightning", but for some reason people think that the bright flash is caused by hot summer
nights. There is not such thing as heat lightning... Check out this video for a great explanation
Click here for the video!
#2 Myth or Fact: Lightning never strikes the same place twice. MYTH
Lightning frequently strikes the same place—especially tall objects like skyscrapers, church steeples,
and radio towers. Check out the video below for further evidence!
#3 Myth or Fact: The risk of a person in the United States being struck by
lightning is approximately 1 in 280,000 people per year. MYTH
Your odds are much better! Your personal risk of being struck each year in the United States is 1 in
700,000. Compared to the Mega Millions lottery, which has a 1 in 175,711,536 chance of winning the
grand prize, you can see you have a significantly better chance of being struck by lightning than
winning the lottery.
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#4 Myth or Fact: If you are caught outdoors during an electrical storm, one of
the safest places to be is in your car. FACT
Here is a video to prove it!
You car is the safest place to be because the metal shell that forms the body and chassis of the car
will behave as a Faraday cage when hit by lightning. A Faraday cage can be described as a metal
enclosure where electricity, when it passes through the metal, tends to stay on the perimeter of the
enclosure rather than passing through it. The electricity resists passing through the center of the car
due to a static cancellation of the electromagnetic field within the metal enclosure.
#5 Myth or Fact: If it is not raining, there is no danger from lightning. MYTH
Lightning can strike several miles away from a thunderstorm. There have been reports of people
being struck more than 10 miles away from a thunderstorm. In fact, a recent tragic death in southern
Illinois occurred at a track meet when lightning stuck a high school pole vaulter. It was reported in
this USA Today article that there was no indication of a nearby thunderstorm and it was barely raining.
#6 Myth or Fact: The rubber soles of your shoes will protect you from harm if
struck by lightning. MYTH
If the lightning was able to travel from the cloud to the ground, a distance measured in miles, through
the air, which is an excellent insulator, it will have no trouble bypassing your 1” rubber soles. Your
shoes offer no protection from lightning—especially when they are wet with rain water. A typical strike
may contain more than 1 billion volts, 30,000 amps and 10 billion joules of energy!
#7 Myth or Fact: People stuck by lightning carry an electric charge and should
not be touched. MYTH
If someone near you is struck by lightning, you can touch them immediately. In fact, you must touch
them! The first thing you should do is check a lightning strike victim’s pulse to see if they need CPR.
Do not fear electrocution! Unlike what some movies (e.g., The Matrix) teach us, humans are not good
at holding large amounts of electrical charge. When lightning strikes a person, the electrical energy is
in and out of that body within one millionth of a second. There is no reason for you to find a stick or
other object to prod the victim first to ensure that you do not get electrocuted. In this video, the woman
was saved because her mother touched her immediately to see if she needed CPR. Watch!
#8 Myth or Fact: A lightning strike can heat the air to a temperature five times
hotter than the Sun’s surface. FACT
At the center of the Sun, hydrogen is fused into helium and this nuclear reaction releases enormous
amounts of energy and heat. At the core, the temperature of the Sun is greater than 11,000,000° C
but as this energy convectively and radiatively spreads away from the center of the Sun toward its
outer shell, it cools to 6,000° C. A typical lightning strike heats the air that immediately surrounds the
bolt to 30,000° C, which is five times the temperature of the Sun’s surface. It is this incredible heat
that creates thunder.
#9 Myth or Fact: A typical lightning strike is 5 km long and 2–3 cm wide. FACT
A common misconception is that the lightning bolt itself is large in diameter but in reality it is about the
width of your thumb.
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#10 Myth or Fact: Locations of lightning strikes can be predicted. MYTH
Although we cannot predict the location of a lightning strike, lightning protection systems can warn
certain locations of the threat of a nearby strike. Using small electric field mills, like the one pictured
above, these lightning protection systems can detect any changes to an electric field produced by the
mill. These changes are typically brought on by thunderstorm activity and when detected, a warning is
sounded. In addition to this, once a lightning strike has occurred, its exact location can be found using
the national lightning detection network. More on this later…
#11 Myth or Fact: It is unsafe to be indoors near appliances or plumbing
during a lightning event. FACT
As demonstrated in the video above many of the materials used in the construction of your home are
excellent conductors, which are not properly grounded. If lightning were to travel through these
conductors, you could easily be electrocuted inside of your home!
#12 Myth or Fact: If you feel your hair stand up on end during an electrical
storm, crouch down low to the ground—you could be struck by lightning.
FACT
The image above was taken of a young woman just moments before she was stuck by lightning. The
electrical field between the ground and a thunderstorm can reach to 3 million volts per meter. This
electric field is more than strong enough to make your hair stand on end. If this ever happens to you,
crouch down low to the ground—don’t run or lie down. More on this later…
Lightning Fatalities
The image below was provided by the National Weather Service and shows the average annual
number of fatalities for multiple hazardous weather conditions. Focus on yellow columns for 30-year
averages, and you will find that lightning fatalities are in third place. On average, approximately 600
people are stuck by lightning in the United States every year but remarkably only about 10 percent of
these people will die from the strike. This has not always been the case though! Over the last 60
years, on average 600 people have been struck. However, back in 1940's and 50's as much as 80%
of them died. The second graph clearly shows that with time the number of deaths from lightning is
descreases thanks in large part to dramatic improvements in medical technology.
Lightning Victim Statistics
If you are fortunate enough to survive a lightning strike, you may suffer from one or more of the
following medical conditions:
1. Memory loss
2. Attention deficit
3. Sleep problems
4. Dizziness
5. Fatigue
6. Hearing loss
7. Confusion
8. Photophobia (fear of having your picture taken)
9. Inability to sit or stand for long periods of time
10. Reduced libido (reduced sex drive)
According to the National Lightning Safety Institute, 98 percent of people who are struck are outdoors.
Statistics over the past 35 years report the following on locations people are struck.
~40% are unreported
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