Lightning
During a thunderstorm, some amazing things
occur, the least of which can be incredible downpourings of rain in a very short
time. In addition, thunder and lightning provides extraordinary air shows, but
also present some dangers. Although
the actual cause of lightning is rather complex, here is a slightly simplified
view.
Cumulonimbus clouds possess a strong
electrical charge which varies as you move upwards through the cloud.
Nearer the base, it is strongly negative, becoming strongly positive in
the upper reaches. The Earth also normally has a negative charge, but during a
thunderstorm this charge becomes positive. The
simplest explanation for this can be found in a comparison to magnets.
Since the lower portion of the cloud and the planet are both negatively
charged, they repel each other, much like two magnets placed with their north
poles together. As the clouds charge becomes more and more negative, so does the
charge on the surface become more positive. These
positive ions will then begin to move to the top of tall trees (and tall hikers
on ridges) as they are attracted to the negative charge in the cloud. Because
air is a very poor conductor, these ions cannot easily travel to one another.
Lightning is the result of this electrical field building up to such an
extent to overcome the poor conductivity of the air.
Suddenly, the insulating capacity of the air breaks down and lightning
occurs. Quite simply when there are
enough charged particles, a sudden violent movement of negatively charged
particles from the cloud to the Earth will occur – lightning. This will continue for up to about a second; until the difference
in charge is reduced sufficiently. The
process of build up will then begin again.
Thunder is the result of an instantaneous
expansion and contraction of the air producing pulses of pressure that we hear
as loud crashing sounds.
Yes, it's true! You can estimate the distance to a storm by counting the number of
seconds between the flash and the crash – however this number must be divided by
five. If the sound and the bold occur
almost simultaneously, it's definitely close byDangers of lightning, Safety tips
When
you're out hiking and a sudden storm blows in – take cover. Mountain hiking can
be exhilarating but it does have its hazards. During a storm, avoid mountain
summits, open stands of trees and shallow caves. The best places are at least a
hundred metres below the summit, inside shallow crevasses, deep caves, the base
of a cliff, or even better, warm and cozy in your car. If you feel your hair
standing on end – make for cover at warp speed.
All Material © Ward Cameron 2005