Lightning

Lightning is a massive natural electrostatic discharge produced during a
thunderstorm.

How Lightning is Formed

Ice crystals inside cumulonimbus clouds rub against one another due to the
strong updrafts in these clouds, thus building up a strong static charge.
Positively charged crystals tend to rise to the top causing the cloud top to
build up a positive static charge and negatively charged crystals and hail
stones drop to the middle and bottom layers of the cloud building up a
negative static charge. Cumulonimbus clouds that do not produce enough ice
crystals usually fail to produce enough static electricity to cause
lightning.

Lightning can also occur as a result of volcanic eruptions, which generate
sufficient dust to create a static charge.

The earth is normally negatively charged with respect to the atmosphere. But
as the thunderstorm passes over the ground, the negative charges at the
bottom of the cumulonimbus cloud cause the positive charges on the ground to
gather along the surface for several miles around the storm. When the
negatives and positives gather in this way, an electrical discharge occurs,
producing the bolt. This discharge usually occurs within the clouds or
between the clouds and the ground. If you feel your hair stand up on end in
a lightning storm beware. The negative charges from the cloud are pulling
the positive charges inside your body to the top of your head and you could
be in danger of being struck.

A bolt of lightning usually begins when a stepped leader stroke is sent out
from the cloud. This leader is invisible to the naked eye. The electrical
charge follows this leader from the ground back to the cloud. The return
stroke is the most luminous part of the strike, and the part that is really
visible. Most lightning strikes usually last about a quarter of a second.
Sometimes several strokes will travel up and down the same leader strike,
causing a flickering effect. Thunder is caused when the discharge rapidly
super heats the air around the strike, causing a shockwave to be sent out.

Various Types of Lightning

All lightning is formed in the same fashion, as stated above, but some
strikes take on particular characteristics, and scientists and the public
have given names to these various types of lightning.

Intracloud Lightning, Sheet Lightning, Anvil Crawlers

Intracloud lightning is the most common type of lightning which occurs
completely inside one cumulonimbus cloud, jumping between different charged
regions within the cloud. Intracloud lightning is commonly known as sheet
lightning because it lights up the cloud and the surrounding sky with a
sheet of light. One special type of intracloud lightning is commonly called
an anvil crawler. Discharges of electricity in anvil crawlers travel up the
sides of the cumulonimbus cloud branching out at the anvil top.

Cloud-to-Ground Lightning, Anvil Lightning, Bead Lightning, Ribbon
Lightning, Staccato Lightning

Cloud-to-ground lightning is a lightning discharge between a cumulonimbus
cloud and the ground initiated by the downward-moving leader stroke. This is
the second most common type of lightning. One special type of
cloud-to-ground lightning is anvil lightning, which is sometimes called
positive charge lightning, since it emanates from the anvil top of a
cumulonimbus cloud where the ice crystals are positively charged. In anvil
lightning, the leader stroke issues forth in a nearly horizontal direction
till it veers toward the ground. These usually occur miles ahead of the main
storm and will strike without warning on a sunny day. They are signs of an
approaching storm. Another special type of cloud-to-ground lightning is bead
lightning. This is a regular cloud-to-ground stroke that contains a higher
intensity of luminosity. When the discharge fades it leaves behind a string
of beads effect for a brief moment in the leader channel. A third special
type of cloud-to-ground lightning is ribbon lightning. These occur in
thunderstorms where there are high cross winds and multiple return strokes.
The winds will blow each successive return stroke slightly to one side of
the previous return stoke, causing a ribbon effect. The last special type of
cloud-to-ground lightning is staccato lightning which is nothing more than a
leader stroke with only one return stroke.

Cloud-to-Cloud Lightning

Cloud-to-cloud lightning is a somewhat rare type of discharge lightning
between two or more completely separate cumulonimbus clouds.

Ground-to-Cloud Lightning

Ground-to-cloud lightning is a lightning discharge between the ground and a
cumulonimbus cloud from an upward-moving leader stroke. Most ground-to-cloud
lightning occurs off of tall buildings, mountains and towers.

Heat Lightning

Heat lightning is nothing more than the faint flashes of lightning on the
horizon from distant thunderstorms. Heat lightning was named because it
often occurs on hot summer nights. Heat lightning can be an early warning
sign that thunderstorms are approaching.

Ball Lightning

Ball lightning is described as a floating, illuminated ball that occurs
during thunderstorms. They can be fast moving, slow moving or nearly
stationary. Some make hissing or crackling noises or no noise at all. Some
have been known to pass through windows and even dissipate with a bang. Ball
lightning is a phenomenon only described by those who have witnessed it
occurring.

However, the engineer Nikola Tesla wrote in Electrical World and Engineer,
March 5, 1904 "I have succeeded in determining the mode of their formation
and producing them artificially."

Sprites and Jets

Sprites and jets are electrical discharges that occur high above a
cumulonimbus cloud. They have been found to occur jointly or as a reaction
to a normal discharge lightning. They are only visible for a split second,
making them hard to detect with the naked eye. Photographs of them have been
taken through telescopes mounted on high mountains or buildings aimed at
distant thunderstorms. The most recent pictures and observations of sprites
and jets have been from space aboard the space shuttles and unmanned
satellites mounted with cameras pointed at the Earth's atmosphere.

Streak Lightning

All lightning is streak lighting. This is nothing more than the return
stroke, the visible part of the lightning stroke. Because most of these
strokes occur intracloud, we do not see many of the individual return
strokes in a thunderstorm.

Lightning Facts

A bolt of lightning can reach temperatures approaching 50,000 degrees
Fahrenheit (or about 28000 Kelvin) in a split second. This is hot enough to
cause lightning strikes that hit a loose soil or sandy region of the ground
to fuse the soil or sand into channels called fulgurites. These fulgurites
are sometimes found under the sandy surfaces of beaches and golf courses or
in desert regions. It is one evidence that lightning spreads out into
branching channels when it strikes the ground.

Lightning Safety

Lightning is responsible for approximately 100 deaths a year in the United
States alone. Lightning ranks second only to floods for storm related
casualties in the U.S. every year. Many of these deaths could be prevented
if basic precautions are taken when thunderstorms are expected in an area.
Listening to a radio to keep up to date on storms in the area is the best
way to prepare for safety.

Safer Locations

No place is truly 100% safe in a thunderstorm, but some places are more safe
than others. Larger, better constructed structures are better than smaller
or more open structures. Fully enclosed metal vehicles with the windows
rolled up are good shelters, providing that no contact is made with any
exposed metal inside or outside the vehicle.

When outside, avoid the following:

   * High places and open fields
   * isolated trees
   * unprotected gazebos
   * rain or picnic shelters
   * baseball dugouts
   * communications towers
   * flagpoles
   * light poles
   * bleachers (metal or wood)
   * metal fences
   * convertibles
   * golf carts
   * water (ocean, lakes, swimming pools, rivers, etc.).
   * metal shafted umbrellas

If you find yourself trapped in an open area during a storm, position
yourself close to the ground by squatting with your feet close together.
Since lightning spreads when it hits the ground, you want to minimize as
much surface area between you and the ground. Remember, humans are good
conductors of electricity, and lightning tends to strike at the highest
thing in an area, because electricity will always try to find the shortest
pathway to the ground.

When inside avoid the following:

   * Use of the telephone
   * taking a shower or bath
   * washing your hands
   * doing dishes

(basically anything to do with water)

   * any contact with conductive surfaces with exposure to the outside such
     as metal door or window frames, electrical wiring, telephone wiring,
     cable TV wiring, plumbing, etc.
   * using electrical appliances that plug into the wall
   * being near windows and doors in general