The ionosphere bounces back radio signals transmitted from the earth. This explains why radio signals can reach far away places in the world, because the electromagnetic radio waves bounce back and forwards towards remote places.
These red and blue bouncing radio waves are called skywaves because they bounce against the sky. The distance these waves can reach depends upon the used frequencies and in the way these frequencies are modulated.
This is the reason why there are several reception possibilities on radios [AM, FM etc.]
The Schumann resonance [vibration] frequency exists between the surface of the earth and the ionosphere, which is the border of the magnetosphere.
Schumann resonance frequencies occur because the cavity (space) between the surface of the Earth and the ionosphere behaves as a so called closed waveguide. This means that the waves are behaving as if they stand still within this cavity. This cavity is naturally energized by electric currents which occur during lightning.
The Schumann resonance frequency is a peak frequency in the extreme low frequency range of the electromagnetic field of the earth. This frequency is around 7.83 Hz and changes slightly under influence of lightning and influences of the sun.
The correlation between these Schumann frequencies and brain wave activities was demonstrated at the university of Munich.
The Alpha brain wave activities [between 7 and 14 Hz] are a state wherein a person is relaxed. This explains the use of Schumann frequency for relaxation and sleep improvement.
Many studies have been done showing important relations between solar, Schumann and geomagnetic rhythms. A wide range of health benefits and wellness have been indicated.
Schumann resonance frequency is important for general health purposes being the reason why it is used in selected PEMF devices.