More than 8.5 million lightning bolts occur daily in world. Most frequently, lightning occurs as exchanges between adjacent clouds or between the upper and lower portions of the same cloud; it also occurs as an electrical connection of ionized air from cloud to ground. The sequence of events that leads to lightning discharge is known, but the mechanism for electrification is not.

Sequence of events that leads to the generation of lightning:

a) Large cumulonimbus cloud experiences a separation of electrical charges:

b) Positively charged particles are mostly high in cloud, while negatively charged particles tend to concentrate in base.

c) Growing negative charge in base attracts a growing positive charge on Earth’s surface immediately below cloud.

d) An insulating barrier lies between cloud base and surface.

e) Contrast between cloud base and surface builds to tens of million volts and overcomes the insulating barrier.

f) Finger of negative current flicks down from cloud and meets a positively charge darting upward from the ground, causing lightning.

The cause of lightning is unknown. Most popular theory states that updrafts carry positively charged particles to top, while falling ice pellets gather negative charges and transport them downward. Also it is currently under investigation if cosmic rays from deep space may be involved.

Thunder—an instantaneous expansion of air caused by the abrupt heating that lightning bolt produces.  This expansion creates a shock wave that becomes a sound wave. The time of the distance that lightning is away can be estimated because of the different rates thunder and lightning travel at (speed of sound vs. speed of light).  It is estimated that five-second interval equals about a mile; three-second interval equals about a kilometer.

More Aspects of Lightning