Hazard Warning: Strikes may damage property and cause serious injury or death.
Lightning occurs when there
is an electrical discharge within, or around, a
thunderstorm. Cloud-to-ground lightning occurs when
the electrical charge travels
between a negatively charged
cloud base and the positively
charged ground. This is the most
spectacular variation of lightning,
forming brilliant, jagged bolts
between the sky and the ground.
Each lightning stroke lasts a
fraction of a second. Sometimes a
number of strokes is needed to discharge
the electrical build-up, giving the lightning a
flickering appearance. Often the main stroke
combines with smaller offshoots
that discharge into the air or
inside the cloud.
The ground, and almost
any solid object in connection
with the ground, will conduct
electricity more effectively
than air. This means that
elevated landmasses and tall
objects such as buildings and
trees are prone to strikes.
lightning occurs from the base of
a cloud. However, a rarer form,
known as a positive flash, occurs when positive
charges higher up in a cloud react with negative
ones on the ground, sending a mighty lightning
bolt from the top of the cloud to the ground.
Since the path of this type of stroke is much
longer, the charge has to be far more powerful.
The color of lightning indicates the content
of the surrounding air. The flash will appear red
if there is rain in the cloud, and blue if there is
hail. The presence of a significant amount of
dust in the atmosphere will produce yellow
lightning. White lightning indicates low
humidity; as a result, this is the form of lightning most likely to generate fires on the ground.
Although only about
20 percent of lightning
reaches the ground, strikes
occur somewhere on Earth
over 100 times every second.
In North America, about 400
people are struck by lightning
each year, and about one in
four of these strikes is fatal.
There are a number of
precautions you can take to
minimize your chances of
being hit by lightning during
a storm. If possible, move
indoors. When lightning
strikes a building, it tends
to run along plumbing and
electrical circuits, so you
should avoid touching metal
pipes or using any electrical
equipment, including telephones and computers.
One of the safest places to be is inside a car, as
the car's tyres provide insulation. Aircraft are also
safe, because they are not in contact with the
ground and therefore cannot conduct electricity.
If you are caught outdoors, do not shelter
beneath isolated trees, as they are favorite pathways for the lightning's leader
strokes. Keep clear of metal
objects such as wire fences,
which can conduct electricity
over considerable distances.
Should your hair begin to
stand on end, this may mean
that you are within the area
of positive charge below the
cloud and that a strike is
imminent. If this happens,
crouch on all fours at once
and keep your head low.
Do not lie full-length
on the ground, as this will
increase your contact with
any charges that may be
conducted through the
ground by wet soil.
If someone is struck by
lightning, expert medical
attention should be requested at once and
cardiopulmonary resuscitation attempted.
The greatest myth associated with cloud-to-ground lightning is that it never strikes the
same place twice. The top of the Empire State
Building is struck about 500 times a year and
was once struck 15 times in just 15 minutes.