The Lightning Dictionary.
Anvil Lightning- Often
called a 'bolt from the blue' because it occurs in seemingly cloudless
skies, a cloud-to-ground discharge reaching from the top of a thunderstorm
and arcing away from the main cloud and striking the ground under sometimes
clear skies. It is dangerous because it fools people into thinking the
lightning danger is gone because the storm is not overhead. Watch this
animated image. The long bolt that strikes to the left of the storm cloud
is an example of anvil lightning.
electric current flowing through air, visible as an intensely bright, hot
light. Arcs are similar to lightning in that the current flows through
a channel of ionized air.
Ball Lightning- A
rare phenomenon described as a floating, illuminated sphere that occurs
during thunderstorms. It may move fast, slow or stay stationary, it may
be quiet or produce a hissing or crackling noise, it may pass through windows,
last from seconds to minutes, and disappear slowly or suddenly either quietly
or with a loud bang. No photographs have ever been obtained of ball lightning,
nor have any official accounts been made of it, therefore its existence
is questionable. The only source of information on ball lightning comes
from eyewitness accounts and no scientific information has been obtained,
so ball lightning remains a mystery.
illuminated parts of the stepped leader that are not part of the main channel.
They are only visible during the first return stroke, and are somewhat
dimmer than the main channel.
path of ionized air in which the discharge current flows. It is illuminated
brightly during the discharge.
to a discharge from a cloud into a pocket of charge in the surrounding
to a discharge between two seperate thunderstorms. Not to be confused with
to a discharge between cloud and ground initiated by a downward moving
flow of current down the ionized channel that equalizes the charge difference
between two regions of opposite charge.
word for a short circuit.
to a lightning discharge. (See Stroke)
short circuit of an electrical power line in the form of a bright arc.
glassy formations caused by a lightning strike to sandy soil. The lightning
heats the soil and fuses the soil particles together surrounding the path
of the channel, resulting in a hollow tube-like formation shaped like the
section of lightning that formed it. Artificial fulgurites have been created
using man-made lightning in laboratories. The word fulgurite comes from
the Greek word fulgur, which means lightning.
to a discharge between cloud and ground initiated by an upward moving stepped
Heat Lightning- Distant
flashes of lightning barely visible on the horizon from faraway thunderstorms.
Named so because it is often seen on hot, muggy nights, when conditions
are favorable for thunderstorm development.
to a discharge within a cloud, the most common type. The channel is normally
obscured from view, and the discharge appears to the observer as a sheet
of light in the sky, therefore it is often called Sheet Lightning. (See
process by which air becomes conductive. It is caused by a tremendous charge
difference between two regions of opposite charge, and in the case of lightning
it is the process that starts the discharge. The electrons in the negatively
charged region are so strongly attracted to the positively charged region
that they begin to move through the air towards the opposing charge and
create a conductive channel. The ionized channel is a conducting path for
the lightning discharge. Also called electrical breakdown. (See Leader,
forming channel of ionized air moving towards the opposing charge. It can
move in steps and branch out, (stepped leader) or move continuously in
a single path. (See Stepped Leader, Ionization)
Lightning Rod (Lightning Protection
System)- A lightning protection device designed
to intercept a strike and divert it safely to ground, avoiding structural
damage to buildings, boats, and other vulnerable objects. A lightning rod
system consists of metallic rods, heavy-duty cable, and a solid grounding
terminal. The cable connects the lightning rods to ground. Lightning rods
do not attract lightning, they simply provide a safe path for the lightning
current to flow.
Power Flash- Bright
electrical arcs from power lines, transformers, or other electrical equipment,
usually used to describe those caused by lightning, tornadoes, high winds,
or winter weather.
Return Stroke- The
flow of current (discharge) through a ionized channel. The return stroke
is brightly illuminated and is the source of thunder. Many times there
will be more than one return stroke through the same channel , making the
lightning seem to flicker. (See Streamers)
waves produced by a lightning discharge. They can be heard with an A.M.
Sheet Lightning- Name
for the sheet of light in the sky from an intracloud discharge.
Shock Wave- The
rapid expansion if air caused by the sudden and extreme heating of the
air in a lightning channel during a return stroke. The shock wave continues
outward for a few hundred yards, moving faster than the speed of sound,
and then slows to a sound wave, heard as thunder. The shock wave from an
extremely close lightning strike can knock a person off his/her feet, and
cause hearing damage and/or other injury. These shock waves can also damage
objects directly struck or nearby objects. (See Thunder)
Sprites and Jets- Electrical
discharges that occur high above active thunderstorms. They have been found
to occur in conjunction with and/or as a reaction to a normal cloud-to-ground
lightning discharge. They are swift and faintly lit, making them almost
invisible to the naked eye. Observations of sprites and jets have been
made by placing a telescope on a high mountain and aiming it above thunderstorms
occuring hundreds of miles away. For more information and photos on sprites
St. Elmo's Fire- Name
given to the blue-green glow around objects (particularly on airplanes
or the masts of ships) dring a thunderstorm. St Elmo's fire is thought
to be a form of corona discharge caused by the high electrical potential
in a thunderstorm.
Stepped Leader- Name
for the downward moving action of electrical breakdown that propagates
from the base of the cloud towards the ground. It splits into more and
more branches as it moves downward, and the branch that reaches an upward-moving
leader from an object on the ground first becomes the path for the return
stroke. The stepped leader is named so because its propagation moves in
in steps, moving through the air in short bursts. The stepped leader illuminates
dimly after each 'step', but it is not visible because the entire process
occurs so fast and so close to the bright return stroke that the human
eye cannot see it. However, it has been photographed with a streak camera.
Stepped leaders can also start from the ground and move upward. (See Streak
Streak Camera- a
special camera used by researchers that can take photographs of several
special lightning features on one piece of film. It works by moving a length
of film rapidly behind the camera lens with high-speed motors, allowing
each step of a lightning flash to be recorded side-by-side on the same
photograph. Streak cameras have been used to photograph stepped leaders
and multiple return strokes.
small intracloud discharges that accompany a larger lightning flash that
'feed' additional charge to the larger flash channel, initiating another
return stroke along the larger channel. This process can repeat many times
and is the cause of a lightning flash appearing to 'flicker' on ond off.
Strike Point- referring
to the object on the ground that was the location of the termination of
the lightning channel. In layman's terms, it's what the bolt hit.
to the flow of current through a lightning channel.
sound waves produced by the explosive heating of the air in the lightning
channel during a return stroke. It originates as shock waves close to the
channel, and moves radially away from the channel. Thunder changes in pitch
with varying distances from the channel. The closer one is to the lightning
flash, the more high-pitched and 'crackle-sounding' the thunder. The further
away, the more low-pitched and 'boom-rumble' sounding it is. Thunder rumbles
and crackles because the lightning channel is crooked and jagged, causing
the sound waves to arrive at the hearer at different times and directions.
If lightning strikes closer than around 300 feet, the observer will hear
one loud, startling, high-pitched bang which is not 'sound wave' thunder,
but the shock wave, sometimes preceded by a faint crackling noise from
a yet to be determined source. (See Shock Wave)
Voltage Gradient- The
surge of voltage through the ground raidially outward from the lightning
strike point. The voltage gradient can electrocute anyone standing on the
ground close to a lightning strike. This is often how lightning injuries
occur to people or animals who are near a lightning strike but are not
directly hit. The reason that standing under or near a tree during a storm
is dangerous is due mainly to the voltage gradient. Even if the main lightning
channel flows entirely through or along the tree and does not jump over
and hit whoever is standing there, the resulting huge surge of current
through the ground surrounding the tree will give a nasty shock to anyone
touching the ground nearby. The reason the term 'gradient' is used is because
the voltage in the ground is lower with increasing distance from the strike
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