>>1923963
>The ionosphere does not ring audibly,
"electromagnetic ringing of the ionosphere"
I know that electromagnetic waves are not audible.
the Schumann resonances are standing waves and associated harmonics of those fundamental frequencies in the cavity formed between the surface of the Earth (a conductor) and the ionosphere (a conductor). The limiting factors on the electromagnetic waves are the size of the cavity and the qualities of the boundaries. The Earth reflects some frequencies, absorbs some and allows others to pass thru. Much like glass only allows certain frequencies to pass thru while reflecting or absorbing others. The ionosphere is much the same in regards to electromagnetic waves, it reflects some, absorbs some and allows others to pass thru.
All of these factors determine which frequencies will resonate in the cavity and which ones won't.
As a general rule the lower frequencies are reflected better than higher. The ionosphere for instance will reflect a 3Mhz ham signal such that it can bounce between the ground and ionosphere all the way around the globe while a 300Mhz signal just passes straight thru it in a straight line.
I agree that the correlation between the human brain waves and the Schumann harmonics is quite strong.
However correlation =/= causation
>I'm not positive on your questions about the ionosphere but I believe it's parameters are determined by cosmic rays.
the current scientific consensus is that the ionosphere is a product of the charged particles emitted by the sun being trapped by the Earth's magnetic field.
The ionosphere does change size, shape and density over time.
The day side vs night side ionosphere are quite different, ask any Ham radio operator.
The globe of the Earth is surrounded by a spherical shell of the ionosphere. The dayside is closer to the Earth and does not have as many charged particles per cubic as the night side. The differences are small but measurable.
The sun being the source of the charged particles and having a known set of cycles that cause variation in the solar output over many years / decades.
The lesser solar output of charged particles due to the solar minimum would cause the Earth's ionosphere to shrink. A smaller cavity has a higher resonant frequency.