Interesting Lightning phenomenon - Schumann Resonance

 There are 50-100 lightning strikes around the world every second! This is because at any given moment there are around 2000 storms taking place. Every bolt of lightning creates electromagnetic radiation in the form of EM waves, but an interesting thing happens between the ground and the ionosphere, which is a layer in the atmosphere consisting of a global layer and shield of ions - it forms a resonance cavity for those EM waves (i.e. the em waves are trapped between the ground and ionosphere). 

Some of the waves, at certain frequencies, can overlap and add up, sort of like sound waves can overlap and resonate in musical wind instruments, forming what's called the Schumann resonance. This is something scientists can measure anywhere around the world! And the resonance depends on the number of lightning strikes. By measuring this at different times of the year, and over many years, it is another measure of global warming, since the frequency of lightning strikes is dependent on the average air temperature. The measurements are yet another confirmation of increased warming, because this is reflected in the comparisons of Schumann measurements over many years.

Nature is cool!