The space between the earth’s surface and the ionosphere comprises a large resonant cavity, which has the ability to output energy at a specific frequency. Like any resonant cavity, the frequency of the energy depends on the size of the cavity. Larger size translates to lower frequency, i.e. longer wavelength.
The ionosphere is composed of atoms that have had electrons forcibly knocked out of orbit by the strong ambient solar radiation. When a neutral atom loses an electron, it becomes a positively charged ion. The ionosphere is highly reflective, forming the upper boundary of the Schumann resonant cavity.
A point to consider is the fact that energy from an outside source must be injected into the cavity if there is to be an output. A laser is similar, where the outside energy is introduced by means of a laser pump, powered by an energy source ranging from an AAA dry cell to a nuclear reactor.
In Schumann resonance from the large ground-to-ionosphere cavity, the frequency is low with a fundamental at 7.83 Hz. The energy source is moderate, with power coming from naturally occurring lightning.
The fundamental is a standing wave, caused by interference between waves reflected back and forth at the cavity’s resonant frequency. Its wavelength is equal to the earth’s circumference.
Due to the low frequency, it has been difficult to differentiate Schumann resonances from background noise. The Schumann resonances are not high-powered events; the accompanying magnetic field is far smaller in amplitude than the earth’s magnetic field. For this reason, it takes specialized equipment to detect these phenomena. Sensitive antennas and receivers, suitably tuned, are connected to high-impedance amplifiers, with electromagnets consisting of many turns of super-fine wire wound about soft iron cores.
two directions perpendicular to each other to account for
the polarization of the magnetic waves. The signal has a low amplitude, so coils in the range of 10k turns with high-permeability cores are necessary.
The primary application for this instrumentation is to measure and record global lightning activity. Lightning on planets other than earth and on Titan, the largest of Saturn’s moons, is suggested in some cases by observations from earth of radio emission spectra consistent with Schumann resonances. But actual confirmation will await closer observation because of the relatively weak nature of the manifestations.
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