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| Kinds of lightning strike |
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All occurrences within the lightning
strike are explained in the previous chapter, but we explained them for
one kind of lightning strike only. We assumed that lightning starts in
the cloud and that downward stepped leader caries negative charge. In
the areas with moderate climates that is what usually happens (in 80 or
90 percent of all cases). Other than that there are other distributions
of charges in the clouds and they cause different kinds of discharge.
If we take a charge and a direction into consideration we could sort them
in four groups:
positive descending lightning, negative descending lightning, positive ascending lightning and negative ascending lightning. Ascending lightning start on some object on the ground and rise towards oppositely charged cloud. They are relatively rare. Lightning currents are measured for different kinds of lightning and results could be presented with diagrams. They show the changing of current through the time within one discharge cycle. Negative descending lightning is the most common. Its current weakens and almost whole occurrence is over after 100ms. Descending positive lightning is rare. Its current impulse last longer, but the time to reach its peak value is longer too. |
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