—Lancaster Farming. Saturday, Oct. 2. 1976
94
By DIETER KRIEG
EDITOR’S NOTE - This ia the eighth report on the force*
which shape our weather.
“Whooooooo," my little 2-ycar old son exclaims excitedly
when he sees a flash of lightning in the sky “ Look at that'" A
bit frightened, but still fascinated, his 4-ycar old brother joins
him and watches Nature's fireworks "Sec the big light,
Daddy’" the older one might ask, while the little fellow
points his little fingers towards the sky and says "big noise "
A thunderstorm - lightning and thunder - is indeed Nature’s
most awesome aerial show. While it’s fascinating to a
degree, to most of us it has always been something more than
that. Usually it’s frightful, and why not. Lightning brings on
more destruction each year than either hurricanes or tor
nadoes and an average of 150 Americans are killed by it
annually. And then there are the bams and houses which are
ignited by it, and livestock that’s killed.
Understanding lightning is not easy, the experts admit, but
they do offer some theories. Last week’s “Weather Report”
told of how the forces of Nature are at work to produce the 100
million volts which are involved in a massive thunderbolt
being released. This week an explanation is offered as to how
that electrical current leaps from cloud to ground, or cloud to
cloud, or ground to cloud. The information which follows
comes directly from a publication issued by the National
Oceanic and Atmospheric Administration, Washington, D.C.
“Lightning occurs when the difference between the
positive and negative charges—the electrical potential—
becomes great enough to overcome the resistance of-the
insulating air, and to force a conductive path for current to
flow between the two charges. Potential in these cases can be
as much as 100 million volts. Lightning strokes represent a
flow of current from negative to positive (in most cases), and
may proceed from cloud to cloud, cloud to ground, or, where
high structures are involved, from ground to cloud”.
“The typical cloud-to-ground stroke we see most
frequently begins as a pilot leader, too faint to be visible,
advances downward from the cloud, and sets up the initial
portion of the stroke path. A surge of current called a step
leader follows the pilot, moving 100 feet or more at a time
toward the ground, pausing, then repeating the sequence
until the conductive path of electrified (ionized) particles is
near the ground. There, discharge streamers extending from
the ground intercept the leader path and complete the con
ductive channel between ground and cloud charges. When
this path is complete, a return stroke leaps upward at speeds
approaching that of light, illuminating the branches of the
descending leader track. Because these tracks point
downward, the stroke appears to come from the cloud. The
bright light of the return stroke is the result of glowing atoms
and molecules of air energized by the stroke.”
“Once the channel has been established and the return
stroke has ended, dart leaders from the cloud initiate
secondary returns, until the opposing charges are dissipated
or the channel is gradually broken up by air movement. Even
when luminous lightning is not visible, current may continue
to flow along the ionized channel set up by the initial step
leader.”
“Ground-to-cloud discharges are less frequently observed
than the familiar cloud-to-ground stroke. In these cases, step
leaders generally proceed from a tall conductive or
semiconductive structure to the clouds; the initial leader
stroke is not followed by a return stroke from the cloud,
possible because charges are less mobile in the cloud than in
the highly conducting earth. Once the conductive path is
established, however, current flow may set up cloud-to
ground sequences of dart leaders and returns.”
“Thunder is the crash and rumble associated with light
ning, and is caused by explosive expansion of air heated by
the stroke. When lightning is close by, the thunder is a sharp
explosive sound. More distant strokes produce the familiar
growl and rumble of thunder, a result of sound being
refracted and modified by the turbulent environment of a
thunderstorm. Because the speed of light is about a million
times that of sound, the distance (in miles) to a lightning
stroke can be estimated by counting the number of seconds
between lightning and thunder, and dividing by five.”
“Lightning comes in many forms. Streak lightning, a
Member Chosen
OLEY, Pa. - Scott Alan
Hauseman, Oley, was
recently granted a junior
membership m the Brown
Swiss Cattle Breeders’
Association of America.
According to National
Secretary Marvin L. Kruse
of Beloit, Wis., junior
memberships give boys and
girls who have had their
ninth birthday before
January 1 of the current
calendar year, and who have
not had their 19th birthday
before this base date, the
privilege of registering in
dividually owned offspring
from Brown Swiss females
at national membership
rates.
The national secretary
reports that Brown Swiss
registrations have shown an
increase each year for the
past four years. He states
Nature’s fireworks explained
that the reason for this
growth is that Brown Swiss
have a wide range of
adaptation and produce a
large volume of market milk
high m protein. He adds that
registered Brown Swiss offer
a challenge to a dairyman’s
abilities and provide a
greater return on his in
vestment m time, labor, and
money.
TRY A
CLASSIFIED
AD!
smgle or multiple line from cloud to ground, is the form seen
most frequently. Forked lightning shows the conductive
channel. Sheet lightning is a shapeless flash covering a broad
area, often seen cloud-to-cloud discharges. Heat lightning is
seen along the horizon during hot weather, and is believed to
be the reflection of lightning occurring beyond the horizon.
Ribbon lightning is streak lightning whose conductive
channel is moved by high winds, making successive strokes
seem to parallel one another. Beaded lightning appears as an
interrupted stroke.”
“Ball lightning is in some ways the most interesting—and
most controversial—form. As reported, ball lightning ap
pears as a luminous globe, toroid (doughnut-shape), or
ellipsoid which hisses as it hurtles from cloud to earth,
maneuvers at high speeds, rolls along structures, or hangs
suspended in the air.”
“The electromagnetic impulses of a lightning stroke
produce whistlers—gliding tones which travel along lines of
force in the earth’s magnetic field from their lightning source
m one hemisphere to a similar point in the opposite
hemisphere, often echoing back and forth several times.
Their sound is something like the whistle of World War II
bombs, occasionally modified in a way that produces musical
variations.”
“The dual character of lightning—it is a carrier of high
currents and produces destructive thermal effects—makes it
doubly dangerous. The current peaks, which may reach
magnitudes of 200,000 amperes or more, produce forces
which have a crushing effect upon conductors, and which can
build to explosive levels in nonconducting or semiconducting
materials like wood or brick. The continuous current
produces heat, and is responsible for the numerous fires
attributed to lightning."
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