A broadband electromagnetic sources, such as lightning, excite the cavity forming a resonant state provided the average equatorial circumference is approximately equal to an integral number of wavelengths of the electromagnetic waves. This phenomenon, known as Schumann resonance (SR), corresponds to electromagnetic oscillations of the surface-ionosphere cavity. There are about 2000 thunderstorms taking place on Earth at every moment of time and approximately 50 lightning occurrences every second. Each lightning event creates electromagnetic waves that begin to circle around the Earth caught between the Earth surface and the lower levels of the ionosphere.

A wave which flows around the Earth reaches itself in such a manner that it completely coincides with itself (i.e. crest and throughs are perfectly alligned) and the resonance phenomenon develops such that the amplitude of the original wave is amplified.

The Earth can be regarded as a nearly conducting sphere, surrounded by an atmosphere which is essentially a thin dielectric layer that extends up to the ionosphere, for which the conductivity is also substantial.

Atmospheric electric discharges, e.g. lightning, generate electromagnetic waves that propagate between the surface and the lower boundary of the ionosphere (~100 km). These two layers form a resonant cavity, which supports both longitudinal and transverse electromagnetic waves. The induced standing electromagnetic waves have wavelengths related to the radius of the cavity. The average measured frequencies of the five lowest wave modes are, approximately, 7.8, 14.3, 20.8, 27.3, and 33.8 Hz, which fall in the Extremely Low Frequency (ELF) range.

Historical perspective

The phenomenon is named after the German electrical engineer Winfried Otto Schumann who applied the resonant cavity model to the Earth-ionosphere cavity in 1952 and published the obtained results in several papers [Schumann, 1952]. Although Schumann initiated the modern study of ELF propagation two names emerge as the scientists who knew of at least the lowest ELF mode around the Earth.

The scientists are Nicola Tesla, Serbian-American inventor, physicist, and engineer who studied similar phenomena at the beginning of the 20th century (1900-1905), and George Francis FitzGerald, the Irish theoretical physicist 1893, who actually should be considered as the first to theoretically predict this phenomenon.

There are some claims that Tesla actually observed the resonance, however as in this and many other cases related to Tesla’s work, there is no written evidence for such claims. Tesla proposed that the Earth itself could be set into a resonant mode at frequencies of the order of 10 Hz. He suggested that energy was reflected at the antipode of his Colorado Springs transmitter in such a manner that the standing waves were formed. In the US patent 787 412 filed on May 16, 1900 and issued April 18, 1905, Tesla writes:

For the present it will be sufficient to state that the planet behaves like a perfectly smooth or polished conductor of inappreciable resistance with capacity and self induction uniformly distributed along the axis of symmetry of wave propagation and transmitting slow electrical oscillations without sensible distortion and attenuation. Besides the above three requirements seem to be essential to the establishment of the resonating condition.

First. The earth’s diameter passing through the pole should be an odd multiple of the quarter wavelength—that is, of the ratio between the velocity of light—and four times the frequency of currents.

Second. It is necessary to employ oscillations in which the rate of radiation of energy into space in the form of Hertzian or electromagnetic waves is very small. To give an idea, I would say that the frequency should be smaller than twenty thousand per second, though shorter waves might be practicable. The lowest frequency would appear to be six per second, in which case there will be but one node, at or near the ground-plate, and, paradoxical as it may seem, the effect will increase with the distance and will be greatest in a region diametrically opposite the transmitter. With oscillations still slower the earth, strictly speaking, will not resonate, but simply act as a capacity, and the variation of potential will be more or less uniform over its entire surface.

Third. The most essential requirement is, however, that irrespective of the frequency of wave train should continue for a certain interval of time, which I have estimated to be not less than one-twelfth or probably 0.08484 of a second and which is taken in passing to and returning from the region diametrically opposite the pole over the earth’s surface with a mean velocity of about four hundred and seventy-one thousand two hundred and forty kilometers per second.

More on the physical and engineering aspects of SR

The fundamental SR wave mode approximately corresponds to a wave with a wavelength equal to the circumference of the Earth, about 6500 km. Transverse resonance is mostly a local phenomenon that contains information on the local height and conductivity of the lower ionosphere and on thunderstorm activity in the vicinity. SR is not the internally-generated resonant frequency of the planet Earth, which is 10 Hz as Tesla discovered.

SR is electromagnetic oscillations, the Earth’s global electric circuit, consisting of the frequencies that play through the cavity between the Earth’s surface and ionosphere. The ionosphere is a highly-conductive region of cosmic plasma [Nikolaenko and Hayakawa, 2014]. The space between Earth and the ionosphere is a closed cavity between that can sustain quasi-standing waves at wavelengths of planetary dimension.

Electrical conductivity in the atmosphere is caused largely by cosmic rays. Conductivity increases exponentially with altitude because of the lower atmosphere buffers collision frequency.

The ionosphere begins about 90 kilometers out from the Earth’s surface and extends out over 300 kilometers. It consists of charged particles constantly exposed to unshielded ultraviolet radiation from the Sun which breaks down molecules and atoms causing the resulting highly charged ions and free electrons to fill the ionosphere creating a “spectral power station”. Lightning radiates broadband (i.e. of large frequency extent) EM fields that spread laterally into the cavity and the resonant spectrum is the superposition of global lightening discharge.

Global thunderstorms excite the Schumann resonances, which can be observed around 7.8, 14, 20, 26, 33, 39 and 45 Hz [Nikolaenko and Hayakwa, 2014]. These values are constant and may be changed only if our planet changes its diameter. Other sources of SR include (1) the vertical component of intercloud and intracloud discharges, (2) an auroral electrojet that flows horizontally within the upper boundary of the cavity at altitudes of approximately 100 km and (3) ELF whistlers, which are narrow signals believed to originate as plasma drift waves in the dayside magnetosheath and to enter the earth-ionosphere cavity through the polar cusp.

There are many reasons why ELF electromagnetic waves are useful. Foremost is the fact that the penetration of energy into conducting media is improved as the frequency is lowered. Also because of the extremely long wavelength (as already mentioned a wave of Schumann frequency f =7.83 Hz has the wavelength of 6500 km, the circumference of the Earth), the conventional fine scale structure of the medium does not seriously distort the wavefronts nor attenuate the signals to any extent. On the other hand, certain properties of the medium that are invisible to higher frequencies play a role in the determination of the propagation characteristics.

Occasional atmospheric electrical current between the cloud tops and the ionosphere causes sufficiently large transient events, called ELF transients, and excites the earth-ionosphere cavity to amplitude that may exceed the background by factors of 10–20 or more [Nikolaenko and Hayakwa, 2014]. There is evidence that ELF transients coincide with transient optical events (TLEs), such as red sprites (i.e. a transient luminous event at 55–80 km with the life time of few tens of ms) and elves (i.e. a transient luminous event in the altitude range between 70–90 km with the life time shorter than 1 ms).

There are three noise sources that interfere with SR: (1) geomagnetic pulsations, which have much larger amplitudes than those of SR and can interfere with the resonance frequency 7.8 Hz; (2) medium-scale power line radiation and relatively nearby lightning; and (3) small scale local or mechanically induced electromagnetic signals. Such noise data can be integrated as part of ELF data in the SR band because their occurrence rates are quite low.

Besides the engineering aspects which are extremely important for various kinds of communication, SR are extremely important for the human health.

Human health and Schumann resonance

Due to the homeostatic requirements, human beings have a very advanced neurological and physiological systems that must be maintained within the narrow activity ranges. Homeostasis is partly maintained under variable environmental circumstances, such as daily climate cycles, through the use of external reference signals, which serve as the biological clock (more like a metronome) which gives information on temporal activations of specific functions of the organism.

However, there is also a natural ELF electromagnetic signal that also acts as a circadian biological clock [Weaver, 1974]. This signal is part of the Schumann spectrum, its lowest frequency mode of 7.83 Hz, and there is no other known natural signal with the appropriate characteristics.

Experimental and clinical data, in addition to theoretical arguments, suggest that the effects of the magnetic component of the electromagnetic field are more important to the human organism than the electric field because magnetic fields can penetrate freely within tissues. In spite of the fact that the typical amplitude of Schumann resonance signals is in the pico tesla range and seems to be negligible compared to some man-made fields surrounding us, the exposure to low-frequency, low-intensity electromagnetic fields can produce biological effects [Cherry, 2003].

In case the human brain is sensitive enough to discern natural signals in the frequency range of the first SR mode or artificially generated 7.8-Hz electromagnetic fields from the background noise, human response to Schumann resonance would make a good health indicator.

A large number of studies have identified significant physical, biological and health effects associated with changes in Solar and Geomagnetic Activity (SGMA). Variations in solar activity, geomagnetic activity and ionospheric ion/electron concentrations are all mutually highly correlated and strongly linked by geophysical processes. A key scientific question is, what factor is it in the natural environment that causes the observed biological and physical effects?

The effects include altered blood pressure and melatonin levels, increased cancer, reproductive, cardiac and neurological disease and death. It is found that the Schumann resonance signal is extremely highly correlated with the solar geomagnetic activities and the physical mechanism which responds to the fluctuations in the solar geomagnetic activities is the resonant cavity in which the Schumann Resonance signal is formed. This strongly supports the Schumann Resonance signals as the biophysical mechanism which is directly correlated with the solar geomagnetic activity.

Because of its strong similarity to the human EEG spectrum and ample evidence that environmental signals of the same frequency range interact with brains, there is an abundance of evidence that Schumann resonance frequency acts as a metronome for various human physiological activities.

The brain is a large origin of extremely low frequency (ELF) signals that are transmitted through the body via the nervous system, which is sensitive to magnetic fields. Brainwaves and natural biorhythms can be captured by strong external ELF signals, such as stationary waves at Schumann resonance. Entrainment, synchronization, and amplification leads toward coherent large-scale activity.

Consequently, resonant standing waves emerge from the brain, which under specific conditions facilitates internal and external bioinformation transfer, via ELF electromagnetic waves [Nikolaenko and Hayakwa, 2014]. These SR waves, exhibit nonlocal character and nearly-instant communication. The rhythms and pulsations of the human brain reflects those of the resonant properties of the terrestrial waveguide cavity. This natural frequency pulsation represents an average of global readings, much like EEG is an average of brainwave readings. SR actually fluctuates, like brainwaves, due to geographical location, lightning, solar flares, atmospheric ionization and daily cycles [Nikolaenko and Hayakwa, 2014].

EEG frequency bands include Theta waves (3.5-7.5Hz); Delta (less than 4Hz), Alpha (7.5- 13Hz); Beta (14-30Hz), and Gamma (higher than 30Hz); The ranges of these waves overlap one another along the frequency spectrum by 0.5 Hz or more. These frequencies are linked to behaviors, subjective emotional states, physiological analogs, etc. Clinical improvement with EEG biofeedback results in improved neuro regulation in the basic functions by exerting influence to their underlying rhythmic mechanisms.

Schumann’s resonance forms a natural feedback loop with the human mind/body. Our brains and bodies developed in the biosphere which was conditioned by the cyclic pulse defined by the Schumann resonance. Conversely, this pulse acts as a “driver” of our brains, and may also carry information as well. Functional processes may be influenced and new patterns of behavior boosted through the brain’s web of inhibitory and excitatory feedback networks.

Without an external reference signal biological systems tend to wander into longer period cycles as part of their adaptive flexibility. It is the role of the circadian clock to synchronize the biological cycles with the daily cycles and the role of the Schumann Resonance is exactly this. It is widely recognized that when the SR signal is in its normal range, associated with normal levels of solar geomagnetic activity, the synchronization process is healthy. When extreme levels of SGMA make the intensity and frequency of the SR signal to drift to extreme values, then this is proposed as the mechanism for altering the brain waves, altering the melatonin/serotonin balance, primarily through melatonin reduction during enhanced activity such as solar maximum and solar storms.

The Circadian Cycle

The main endocrine process involved in the daily (circadian) cycle is the melatonin/serotonin system. It initially operates between the pineal gland and the hypothalamus. A specific part of the hypothalamus, the suprachiamatic nucleus, contains the ‘biological clock’. In order to mediate the daily cycle there are high affinity melatonin and serotonin receptors in the brain and throughout the central nervous system. This includes the autonomic and sympathetic nervous systems and melatonin modulates the functional sensitivity of the serotonin receptors.

The cardiovascular system is daily determined by melatonin through receptors in the heart, arteries and lungs. Heart rate variability is used to monitor the autonomic nervous system and reduced heart rate variability is a risk factor for heart disease. There are also melatonin receptors in other vital organs of the body that are part of the daily cycle system.

This includes the pituitary gland which regulates the production of Growth Hormone and Thyroid Stimulating Hormone. Melatonin has direct action in the immune system through the T-Lymphocytes (T-Helper Cells), interleukin-2 and -6 (IL-2. IL-6) and natural killer cells (NKcells) through melatonin receptors on the T-Cells [Reiter, 1994].

This enhances the natural and acquired immunity. Melatonin receptors have been identified in a number of peripheral organs and tissues. For example, melatonin receptors maintain intraocular pressure in the eye. The reproductive organs also have melatonin receptors in the testes, prostate, ovary, mammary gland and other reproductive organs. The fetus has many melatonin receptors so that the maternal melatonin can communicate daily and seasonal cycles in utero.

Through receptors melatonin regulates the daily and seasonal activity. This involves metabolism, respiratory activity, sleep-wake cycle, reaction times, body temperature, blood pressure, heart beat, peripheral blood flow, hormone levels and immune system blood cells. It also involves the humoral organs of the lung, heart, kidney, spleen, liver and lymphocytes of the immune system.

Melatonin is also a highly potent antioxidant that scavenges free radicals from cells [Reiter, 1994]. This implicates that reduced melatonin is associated with neurological, cardiac, reproductive and carcinogenic illness and death [Reiter and Robinson, 1995].

The abundance of published research material suggests that The Schumann Resonance signal is the biophysical mechanism for the health effects of the solar geomagnetic activity because it is detected by the brain where it interacts with the ELF brain waves by resonant interaction with neurons calcium ions and it alters the melatonin/serotonin balance. Consequently, the SR provides an ELF, daily and seasonal synchronization reference signal, a metronome of the biological clock.