General introduction
Lightning naturally occurring spark discharge or
short-lived electric arc.
Some 90% all lightning discharges between cloud
and the ground are negative ground-to-cloud strikes. Lightning involves ex-
change electric charges (electrons gas ions), in
other words, electric currents flow. Depending the
polarity the electrostatic charge, lightning can al-
ternatively start from the ground.
NASA has measured the annual global frequency of
lightning over the period 1995 2003. Lightning discharges can take
place from one cloud another, between cloud
and the ground.
Annual number lightning strikes per km2
between 1995 and 2003
(www. Lightning one the "electrometeor-
s" generally occurs during thunderstorms, where it
is accompanied thunder. The local val-
ues obtained NASA can used determine the
annual number lightning strikes per km² even for
countries that not have their own information on
numbers lightning impulses.
However, the vast majority discharges take place
within clouds, from one cloud another. For risk assessments
according IEC/EN 62305-2, recommended that
these values are doubled.
Here, the lightning begins area negative
charge the cloud and spreads the positively
charged ground.nasa.TBS
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The less common types discharge are:
• Negative ground-to-cloud lightning
• Positive cloud-to-ground lightning
• Positive ground-to-cloud lightning
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9
Chapter General introduction
