The sky is filled with electric charge.
In a calm sky, the + and - charges are evenly interspersed
thoughout the atmosphere. Therefore, a calm sky has a neutral charge.
Inside a thunderstorm, electric charge is spread out differently. A
thunderstorm consists of ice crystals and hailstones. The
ice crystals have a + charge, while the hailstones have a - charge. The
ice crystals are pushed to the top of the thunderstorm
cloud by an updraft.
Meanwhile, the hailstones are
pushed to the bottom of the thunderstorm by its downdraft. Thus, the
thunderstorm's + and - charges are separated into two
levels: the + charge at the top and the - charge at
the bottom.
During a thunderstorm, the Earth's surface has a + charge.
Because opposites attract, the - charge at the bottom of the
thunder cloud wants to link up with the + charge of the Earth's
surface.
Once the - charge at the bottom of the cloud gets large enough to
overcome air resistance, a flow of - charge rushes toward the
earth. This is known as a stepped leader. The + charges of the
Earth are attracted to this stepped leader, so a flow of + charge
moves into the air. When the stepped leader and the + charge from
the earth meet, a strong electric current carries + charge up into
the cloud. This electric current is known as the return stroke of
lightning and is visible to the human eye.
Back to Thunder
and Lightning
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