|Why does lightening occur in rainy times?|
Lightning is coupled to rainy times because
lightning occurs when there are lots of clouds
around. Why does the lightning occur at all? Large
air currents cause water molecules to rise quickly
in large, dark clouds. As the water molecules rise
and turn into ice, they bump into other water
molecules and ice and thus generate static
charges. What ends up happening is positive charge
accumulates at the top of the cloud and negative
charge accumulates at the bottom. Now, the ground
has a combination of positive AND negative charges
to have what is called an average of "0 potential"
but since it is very, very large, it can absorb
discharge from the cloud. When enough negative
charges accumulate at the base of a cloud, the
cloud discharges and we see lightning.
I don't think we know yet exactly what creates
the separation of electrical charges that makes
lightning possible, but it's been seen on Venus
and Jupiter as well as Earth, neither of which has
rain as we normally think of it. Lightning on
Earth happens in towering clouds of great vertical
extent, not in flatter rainclouds, which means
that it probably has something to do with the
updrafts that happen in such large clouds. Again,
so far as I am aware, the true cause of lightning
remains a mystery, but the fact that it happens on
planets that have quite different atmospheres from
the Earth can provide some clues.
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