The Schumann resonances (or frequencies) are quasi-standing electromagnetic waves that exist in the cavity (or space) between the surface of the Earth and the ionosphere. In 1952, German physicist Professor Winfried Otto Schumann of the Technical University of Munich began attempting to answer whether the Earth itself has a frequency – a pulse. His assumption about the existence of this frequency came from his understanding that when a sphere exists inside another sphere, electrical tension is created. Since the negatively charged Earth exists inside the positively charged ionosphere, there must be tension between the two, giving the Earth a specific frequency. Through a series of calculations, he was able to deduce a frequency he believed was the pulse of the Earth-ionosphere space. Two years later, in 1954, Schumann and Herbert König reported reliable and predictable frequencies in the atmosphere that existed in the cavity (or space) between the surface of the Earth and the ionosphere. Though several frequencies occur between 6 and 50 cycles per second, the fundamental frequency they found to be 7.83 Hz.1
This “cavity” is naturally excited by energy from lightning discharges and radio atmospheric signals or sferics. (A sferic is a broadband electromagnetic impulse that occurs as a result of natural atmospheric lightning discharges.) This causes the Earth-ionosphere cavity to "ring" like a bell at specific frequencies, resulting in peaks in the noise spectrum. Schumann resonances are not measurable all the time but have to be “excited” to be observed. They are primarily related to electrical activity in the atmosphere, particularly during times of intense lightning activity. At any given moment, about 2,000 thunderstorms roll over Earth, producing some 50 flashes of lightning every second. Each lightning burst creates electromagnetic waves that begin to circle around Earth captured between Earth's surface and a boundary about 60 miles up. Some of the waves - if they have just the right wavelength - combine, increasing in strength, to create a repeating “atmospheric heartbeat” known as Schumann resonance. This resonance provides a useful tool to analyze Earth's weather, its electric environment, and to even help determine what types of atoms and molecules exist in Earth's atmosphere.2
Lightning photo courtesy of NOAA Photo Library, NOAA Central Library,
OAR/ERL/National Severe Storms Laboratory (NSSL)
The waves created by lightning do not look like the up and down waves of the ocean, but they still oscillate with regions of greater energy and lesser energy. These waves remain trapped inside an atmospheric ceiling created by the lower edge of the "ionosphere" - a part of the atmosphere filled with charged particles, which begins about 60 miles up in the sky. In this case, the sweet spot for resonance requires the wave to be as long (or twice, three times as long, etc.) as the circumference of Earth. This is an extremely low frequency wave that can be as low as 8 Hertz (Hz) - some 100,000 times lower than the lowest frequency radio waves used to send signals to an AM/FM radio. As this wave flows around Earth, it hits itself again at the perfect spot such that the crests and troughs are aligned. Thus, waves act in resonance with each other to pump up the original signal.3, 4
The ionosphere is part of Earth’s upper atmosphere where extreme ultraviolet and X-ray solar radiation ionizes the atoms and molecules thus creating a layer of electrons. It stretches from approximately 60 miles above the surface of the Earth to the edge of space. Other phenomena such as energetic charged particles and cosmic rays also have an ionizing effect and can contribute to the ionosphere. This dynamic region grows and shrinks (and further divides into sub-regions) based on solar conditions and is a critical link in the chain of Sun-Earth interactions. Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers created within the ionosphere, called the D, E, and F-layers. The electron density is highest in the upper, or F region and this region exists during both daytime and nighttime. During the day it is ionized by solar radiation, during the night by cosmic rays. The D region disappears during the night compared to the daytime, and the E region becomes weakened. Highly charged ions and free electrons fill the ionospheric layers creating a “spectral power station”. Schumann frequencies are determined by the size of the Earth-ionosphere cavity and can vary slightly from a variety of other factors, such as solar-induced perturbations to the ionosphere, which compresses the upper wall of the closed cavity.5
When a solar flare occurs, the flare’s X-ray energy increases the ionization of all the layers, including the D layer. Thus, D now becomes strong enough to reflect the radio waves at a lower altitude. So, during a solar flare, the waves travel less distance (bouncing off D instead of E or F). The signal strength usually increases because the waves don’t lose energy penetrating the D layer. However, the strength of very low frequency waves (radio frequencies in the range of 3 to 30 kilohertz) can either increase or decrease during a flare. The signal strength could decrease because the lower the waves reflect, the more collisions, or interferences of waves, there will be because of the thicker atmosphere. These wave collisions can result in destructive interference.