Ball Lightning
SOURCE
Ball Lightning
Many people have reported seeing ball lightning. However no-one is sure
exactly what it is. Some people believe that it is a ball of plasma that is
somehow trapped by strong magnetic fields.
Whatever ball lightning is, many scientists now accept that it is real. Ball
lightning normally appears as a freely floating glowing ball, about the size of
a grapefruit. Sometimes the ball is seen to pass through walls or ceilings. It
does not appear to be dangerous.
Question - Hello, During a thunderstorm a bolt of lightning hit our back
yard. Our neighbors dogs had been killed by the lightning so I went in the back
yard to check on our dogs. I then saw a green glowing object on the ground. I
picked it up and realized that it was a twig (probably pine). It looked
phosphorescent in nature, but I can't be sure. It slowly lost its luminescence
in my hand and looked like an ordinary stick. I am wondering what this might
have been. ----------------- Adam, The phosphorescent green color that you saw
is normally a description of ball lightning. Ball lightning may have rested on
the twig and when you picked it up it had lost most of it's energy (I'm assuming
this since you didn't say that the twig hurt you). However, recent observations
have shown that ball lightning, or the characteristics of it, can also be
produced by a standard lightning bolt hitting the ground. Organic material
(which the twig is), normally soil, can be energized and send out a small ball
lightning. In your case, the twig itself may have been the organic material that
was energized and thus produced the characteristic phosphorescent green color.
David R. Cook Atmospheric Physics and Chemistry Section Environmental Research
Division Argonne National Laboratory
===================================================== Dear Adam- That is an
interesting observation about the glowing twig. Was it the only one, or were
there others..? It is possible that it was caused by a lightning strike, but
there should be more evidence of a strike than one small glowing twig... The
bright flash or electrical current through the twig could possibly chemically
react with some substance in the twig to make it phosphores I suppose, but I'm
not aware of how common or rare this is... Wendell Bechtold, meteorologist
Forecaster, National Weather Service Weather Forecast Office, St. Louis, MO
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Question - I was watching a thunder and lightening storm that was about 10
miles away from me. One lightening strike caused a big, bright blue ball of
light to form at ground level, and then flash away quickly. The bright blue ball
of light looked sort of like an explosion. What was the big bright blue ball of
light? What caused it? > > >Nancy, > >The blue ball of light may
have been an explosion, >but it may have been a strike to an electrical
>facility (power line for instance). I have seen >something similar when
lightning struck a high >power line tower. > >David Cook >Argonne
National Laboratory
Here's a great article on lightning
Lightning
Porter Johnson
Lightning, the thunderbolt from mythology, has long been feared as an
atmospheric flash of supernatural origins; the great weapon of the gods.
The Greeks both marveled and feared lightning as it was hurled by Zeus. For
the Vikings, lightning was produced by Thor as his hammer struck an anvil
while riding his chariot across the clouds. Thunder and lightning are
mentioned several times in the Bible. Here is one especially
graphic reference:
And the LORD shall be seen over them, and his arrow shall go forth as
the lightning; and the Lord GOD shall blow the trumpet, and shall go with
whirlwinds of the south.
Zechariah
9:14, Authorized King JamesVersion
Today, scientific rather than mystical techniques are used to explain
lightning with experimental procedures and replacing intuitive concepts.
Yet, we remain in awe of lightning which still flashes in its mystery, and
rightly so.
G W Richmann, a Swedish physicist working in Russia in 1753, proved
that thunderclouds contain electrical charge, and was killed when lightning
struck him. Benjamin Franklin performed the first systematic scientific
study of lightning during the second half of the 18th century. While
others had noted the similarity between laboratory sparks and lightning, Franklin
was the first to design an experiment that conclusively proved the electrical
nature of lightning. In addition to showing that thunderstorms contain
electricity, by measuring the sign of the charge delivered through the kite
apparatus, Franklin concluded that the lower part of the thunderstorm was
generally negatively charged. Lightning current measurements were made in
Germany over a century ago by Pockels, who analyzed the induced magnetic
field to estimate current values. Lightning research in modern times began with
the measurement of the induced electric field by C T R Wilson, who
won the Nobel Prize in Physics for invention of the Cloud Chamber.
At any time, there are more than a thousand thunderstorms around the
earth, producing some 6000 flashes of lightning per minute.
This continuous discharge occurs because of the build-up of negative charge
high in the earth's atmosphere, and positive charge near the earth's
surface. During a thunderstorm the negative charges migrate to the bottom
of the cloud, while positive charges go to the top. When the negative charge
becomes large enough, it flows to the positively charged ground below.
Questions Concerning Lightning
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What is Lightning?
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When and where is Lightning more likely to
strike?
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What is the energy source for Lightning?
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What determines the color of Lightning?
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Where do the sounds of Thunder come from?
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What is Ball Lightning
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Can Lightning be produced by man?
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What about poems and stories involving Lightning?
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What is Lightning?
Lightning is a transient discharge of static electricity that serves to
re-establish electrostatic equilibrium within a storm environment. A
thunderstorm is a very turbulent environment, with strong updrafts that
transport water droplets up in the cloud, while ice particles descend from the
frozen upper regions. As they collide, electrons shear off the ascending
water droplets and collect on descending ice particles. [A similar effect occurs
when you rub your feet across a carpet before touching a door knob.]
As positive charge at the top of the cloud and negative charge at the bottom
increase, the electric field inside the cloud grows in strength. Because
the atmosphere is a very good insulator, a tremendous charge must be built up
before electric discharge [lightning] can occur. Most lightning occurs
within the cloud itself, because the electric fields within the cloud are
typically much greater than those between the bottom of the cloud and the
surface of the earth Here is a Biblical reference to cloud-to-cloud
lightning:.
For as the lightning, that lighteneth out of the one part under
heaven, shineth to the other part under heaven; so shall the Son of
man be in his day.
Luke
10:18, Authorized King JamesVersion
Cloud-to-ground lightning can involve a transfer of positive charge to the
ground (about 10% of the time). Usually, there is only one stroke
for positive flashes, which most often occur away from the central rain shaft,
and which are generally more damaging than negative flashes. It is
believed that a large percentage of forest fires and power line damage is caused
by positive flashes.
Lightning sometimes strikes the ground and tunnels downward into the earth.
The intense deposition of energy causes the sand particles to come together to
form a tubular crust [the shape of the bolt's path] called a fulgarite,
after the Latin word for lightning. Some fulgarites are more than 3 meters
long. Lightning may flash-heat ferromagnetic materials in minerals above
their Curie temperatures, effectively resetting the magnetic fields
trapped in lava flows. In addition, generates reactive chemicals in the
atmosphere that enhance the production of acid rain.
For more information see the websites
When and where is Lightning more likely to
strike?.
You should avoid Florida, Texas, and North Carolina, the states with the
greatest number of lightning deaths. Especially avoid these states in June
[worst month], followed by August, July, April, and September. Central
Florida is generally regarded as the Lightning Capital of the United States.
The most common situation for a lightning death or injury in Florida was found NOT
to be in the heaviest rain area with lots of flashes, but before of
after the time when rain and lightning was most intense.
Lightning Map of the United States
Avoid open spaces, fields, and ballparks, standing under trees, golf courses
or heavy road equipment, telephone booths, as well as boating, fishing, and
other water-related activities. The deadliest lightning strike ever was of
a Boeing 707 near Elkton MD on 08 December 1963. The plane then
crashed, killing 81 people.
Lightning occurs more frequently over land than over water. According
to NASA's Lightning Imaging Sensor, about 90 percent of lightning
occurs over land, in spite of the fact that 75 percent of the earth is
covered with water. Increased lightning activity over land is most likely
due to enhanced convection, by which water carries excess energy into the upper
atmosphere. Over land there is more ice production, and consequently more
lightning.
For more information see these websites:
What is the energy source of lightning?
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The earth is electrically charged and acts as a spherical
capacitor, with a net negative charge of about 1 million Coulombs,
while an equal positive charge resides in the atmosphere.
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The electrical resistivity of the atmosphere decreases with height up to
about 50 kilometers [called the electrosphere], where it is roughly
constant.
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There is a potential difference of 300,000 Volts between the
earth's surface and the electrosphere, corresponding to an electric field
strength of 6 Volts/meter in the atmosphere.
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Near the surface, the fair weather electric field strength is about 100
Volts/meter.
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A fair weather current of about 2000 Amperes flows continuously.
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The earth's charge would dissipate in less than an hour at this rate, except
that lightning recharges the earth by delivering negative charge back to the
earth.
Lightning is caused by a build-up of charge in the atmosphere, generating
electric fields that cause the formation of an electrical channel through air.
The channel is actually begun with a leader carrying a relatively low charge.
This initial pulse [leader] usually fails to "even out" the charge
imbalance. The resulting unbalanced charge now flows preferentially along
the same path because of the ions created by the leader, to form a "return
stroke" and flow until the charge imbalance is reduced
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Lightning generally has about 3-4 flashes [about 40
microseconds apart], but as many as 26 flashes have been
observed.
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The maximum current in a flash is typically about 30,000 Amperes,
although it can be ten times that large.
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The current in a flash lasts for about 50 microseconds.
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The average peak power per stroke is about 1012 Watts.
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What determines the color of Lightning?
The curious red flashes of light nicknamed elves that flicker above
thunderstorms are powered by lightning. These rings of light appear at
altitudes of about 90 kilometers and move outwards like ripples on a pond.
Elves are cousins of red sprites that occur lower in the stratosphere.
Sprites were identified in the following passage from William Shakespeare:
Now is the time of night
That the graves, all gaping wide
Every one let forth his sprite
In the church-way paths to glide
- A Midsummer Night's Dream: Act
5, Scene 1
What is Ball Lightning?
Ball lightning (boules de fue or foudre spherique in French
and Kugelblitz in German) refers to mobile luminous spheres sometimes
observed during thunderstorms. Most observations of ball lightning are
made during thunderstorm activity, within a few meters of the ground. A
typical ball lightning is about as big as an orange or grapefruit, and lasts a
few seconds. Visual sightings are often accompanied by sound, odor, and
permanent material damage. Here is an unusual incident reported by Morris
(1936):
During a thunderstorm I saw a large, red hot ball come down from the sky.
It struck our house, cut the telephone wire, burnt the window frame, and then
buried itself in a tub of water which was underneath. The water boiled
for some minutes afterwards, but when it was cool enough for me to search I
could find nothing in it.
Very similar, if not identical phenomena, occur in submarines due to
electric discharge of direct current across a circuit breaker, and in high-power
electrical equipment. Ball lightning is sometimes confused with St
Elmo's Fire. St Elmo's fire is a corona discharge from a pointed
conducting object, which must remain attached to a conductor, and which usually
lasts much longer than ball lightning.
For additional information, consult these websites
Where do the sounds of Thunder come from?
Aristotle suggested that thunder preceded lightning, the lightning
being a burning wind produced after the impact of the dry exhalation of a cloud,
whereas Lucretius thought lightning and thunder were created
simultaneously in a collision between clouds. Both were aware that an
observer sees lightning before he hears thunder. Descartes felt that
thunder was due to higher clouds descending on lower clouds, the sound from the
resonance of air between the clouds. It was generally accepted in the
mid-nineteenth century that a lightning discharge produced a vacuum along its
path, and that thunder was caused by subsequent motion of air into the vacuum.
Mershon (1870) suggested that
The electricity in passing from one cloud to another, or to the earth,
decomposes the water in the cloud into its component gases; and the great
heat of the electricity ignites and explodes these gases, and reforms them
into water.
The sound of the explosion was supposedly the thunder. The modern view
of thunder was first proposed by Hirn.
Thunder is the acoustic shock wave caused by the extreme heat generated by a
lightning flash. The temperature of air near a lightning bolt is
about 30,000o Celsius. The air expands expands rapidly,
and when its expansion rate exceeds the speed of sound, a sonic boom [thunder]
results. When the lightning strikes very close by, the thunder will sound
like a loud bang, crack, or snap, with very short duration. As the shock
wave [thunder] propagates from its source, it stretches and becomes elongated.
At great distances, the continuous rumble of thunder may last for several
seconds. Thunder can typically be heard up to 15 kilometers, and
even further on cool, calm, and quiet nights.
Can Lightning be produced by man?
Yes: Try this easy experiment to make your own miniature version of a
lightning bolt.
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Here are some references on research programs to generate lightning strikes:
What about poems and stories involving Lightning?
In the East, early statues of Buddha show him carrying a
thunderbolt with arrows at each end. Indian tribes in North America
believed that lightning was due to the flashing feathers of a mystical bird
whose flapping wings produced the sound of thunder.
English folklore described a number of trees and the relative danger of
being struck beneath them by this adage:
Beware of the oak, it draws the stroke.
Avoid the ash, it courts the flash.
Creep under the thorn (hawthorn), it will save you from harm.
The truth of proverbs such as these has been the subject of a number of
studies which indicated that beech (smooth bark) is a poor conductor of
electricity and oak (rough bark) a good conductor. Of course there are
other factors to consider.
During the middle ages, ringing of church bells was believed to diffuse
lightning, and many medieval bells were engraved with the inscription Fulgara
frango [I break up the lightning]. A medieval scholar discredited this
theory, observing that over a 33 year period there were 386 lightning strikes on
church towers and 103 fatalities among bell ringers.
One of the most profound references to lightning in poetry is the following
stanza written by the American poet Emily Dickinson.
The lightning that preceded it.
Struck no one but myself,
But I would not exchange the bolt
For all the rest of life.
For more information consult the website:
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A lightning bolt generates temperature five times hotter than those
found at the sun's surface.
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The average number of deaths by lightning in the United States is about
89 per year.
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Carnivorous animals will not eat another animal that has been struck by
a lightning strike
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Most brush and forest fires in the Western United States are caused by
lightning..
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The Hindenberg crash was not caused by a hydrogen explosion, but
rather by the paint being ignited by lightning. They had unknowingly
painted it with a highly flammable compound.
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Roy C Sullivan, an ex-park ranger, survived seven different
lightning strikes over the period 1942-1977. Over the years, he lost
his big toenail, burned off his eyebrows, seared his left shoulder, set his
hair on fire, struck his legs, injured his ankle, and burned his stomach and
chest.
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Oak trees are struck by lightning more often than any other tree.
This may be one reason that the ancient Greeks considered oak trees sacred
to Zeus, the god of thunder and lightning.
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The Empire State Building in New York City is struck by lightning
an average of 23 times a year. During one thunderstorm the building
was struck 8 times in 24 minutes.
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If you are in an automobile with the windows rolled up and not in
contact with any of the metal parts when lightning strikes, you are safe.
The car's metal body will conduct the charge to the ground. Contrary
to popular belief, the rubber tires offer no protection.
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Lightning bolt charges can propagate for up to 100 miles; however the
actual channel of lightning is rarely larger than the width of a pen.
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For more details, see these references:
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Martin A Uman, Lightning [Dover 1969] ISBN 0 - 486 - 64575
- 4.
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Lightning Images
While watching the storm from my house in Ealing, I would in several
instances distinctly perceive a flickering appearance of a discharge, and in
one particular case the repetitions were at least five or six in number,
just sufficiently slow for the eye to detect the variations in brightness
without removing the impression of a single flash. ... the camera was moved
in a horizontal plane about the lens as a center at the rate of once to and
fro in about three quarters of a second. ... I hoped, by the camera moving,
to be able to separate the successive components of the flashes, and in this
I was fortunately successful.
H H Hoffert (1889)
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