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THUNDER AND LIGHTNING
A flash of light, followed
by a low rumble or a loud crash; a thunderstorm is in the area. A thunderstorm
has an intense updraft and downdraft within a cumulonimbus cloud. Water and
ice particles circulate within the storm. The combination of the storm's vertical
motions and the particles help to create differing electrical charges within
the cumulonimbus cloud. Lightning occurs when electricity travels between areas
of opposite electrical charge.
A flash of lightning can
be seen when the attraction of the positive and negative charges becomes strong
enough to overcome the air's high resistance to electrical flow. In cloud to
ground lightning, negative charges build up in the base of the cloud, while
positive charges at the ground, accumulate atop taller objects such as trees.
When the attraction of the charges becomes too great, negative charges zigzag
their way to the ground as a "stepped leader." When the two different
charges meet, a powerful electric current begins to flow. A return stroke of
positive charges travels rapidly up the leader to the cloud, and this creates
the flash of lightning. This process can repeat itself several times along the
same path in less than half a second, making lightning flicker.
The tremendous energy released by the lightning is turned into heat and sound
waves. Lightning heats the air to a temperature almost 5 times hotter than the
sun in a fraction of a second. The air quickly expands and contracts. This causes
air molecules to move rapidly, which creates sound waves - the thunder.
Since the speed of sound
is slower than the speed of light, lightning will always precede thunder even
though they occur instantaneously. Sharp and loud cracks of thunder originate
from a nearby thunderstorm, while low rumbles are generated by distant storms.
One can determine the distance of thunderstorm by counting the seconds between
the lighting and thunder; five seconds corresponds to about one mile.
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