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Dangerous and staggering at the same time: Lightning

Lightning is a hot affair, because the surrounding air will be heated up to
30,000 degrees Celsius. The air molecules start to glow – a phenomenon
we call "lightning". Only this way it becomes visible that high voltages
of up to 100 million volts and currents up to  30,000 amperes dominate
the atmosphere.

This poses the question of the origin of lightning. It arrives with the
thunderstorms when warm humid air masses pile up several kilometers
in the atmospheric heights. The sun is responsible for this: By warming
up the soil it causes humidity to ascend. The warmer the air the faster
this happens.

With the updraft of the air a cooling process sets in and the humidity condensates. Tiny water droplets and ice crystals emerge and form clouds.

But only when a charge separation takes place within the clouds, lightning finally evolves. Strange enough, up to now, scientists are not sure as to how this happens in detail.

Presumably processes in the smallest scale are responsible. The heavy water droplets and the lighter ice crystals are carried upwards by thermal updrafts. On the other hand graupel, a soft ice-water mixture, falls downwards.
The collision of these particles results in a charge separation, some particles lose electrons and become positively charged and others gain electrons, hence become negatively charged.

Therefore a voltage builds up within the cloud, discharging itself in form of lightning after exceeding a certain amount of approx. 3,000,000 V/m.

In doing so the lightning may take different directions: From cloud to ground or vice versa from ground to cloud or even discharge itself within the cloud.

Most frequently we observe a negative cloud-to-ground lightning that flashes from a positively charged area within the cloud to a negatively charged area
on the ground.

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