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Frequency of the Lowest Electromagnetic Waves

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Bibliographic Entry Result
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Ulf Waves (geomagnetic pulsations). Space Physics Textbook. Oulu, Finland. "Geomagnetic pulsations, i.e., ultra-low-frequency (ULF) waves cover roughly the frequency range from 1 mHz to 1 Hz, i.e., from the lowest the magnetospheric cavity can support up to the various ion gyrofrequencies." 0.001 Hz
"Electromagnetic Radiation." Macmillan Encyclopedia of Physics. New York: Macmillan, 1996: Vol. 2, 431.
Table 1. Electromagnetic Radiation
TypeFrequency (Hz)Wavelength (m)
< 10 Hz
Stoupel, Eliyahu. Clinical Cosmobiology. Canadian Medical Meteorology Network. Reprint from Bio-Electro-Magnetics Institute: Vol. 1, No. 1 (Spring 1989). "The temporal intensity variations, or pulsations, occur over a wide frequency range from DC levels changes; to frequencies much below one cycle per second (micropulsations); to brain wave frequencies (1-30 cycles per second); and higher frequencies." < 1 Hz
ULF Pulsations. Insitut Für Geophysik and Meteorologie Tu Braunschweig (IGM Research). "The first observation of ULF waves was published by Balfour Stewart in 1861 using magnetographs at Kew Observatory. He was describing pulsations of the geomagnetic field, with an amplitude of roughly 0.2 % of the background field, and frequencies in the range between 30 mHz and 3 mHz. Such events became known as geomagnetic micropulsations." 0.003 Hz
Waters, C.L. ULF Resonance Structure in the Magnetosphere. University of Newcastle. "The upper frequencies of the ULF band arise from the various ion gyrofrequencies while the lower frequencies (1-100 mHz) are oscillations of dimensions of order the size of the magnetosphere." 0.001 Hz

Electromagnetic waves are periodic waves produced by accelerated charge. The electromagnetic spectrum shows the range of electromagnetic waves from lowest to highest frequency. Several textbooks cite the frequency of the lowest electromagnetic waves on the order of 102 Hertz (Hz) and such waves are classified as Extremely Low Frequency (ELF). However, it has been discovered that the frequency of the lowest electromagnetic waves is on the order of the 10−3 Hz (millihertz or mHz) and are known as micropulsations.

In some sources, these micropulsations were categorized as part of the Ultra Low Frequency (ULF) range. Conversely, several sources classified ULF waves as having a higher frequency (103 Hz) than ELF waves. It seems that there has been no standardization to the classifications in the electromagnetic spectrum. An interesting observation to note is that those sources that refer to micropulsations as part of the ULF band are international (e.g. Australia, Germany, Finland, and Denmark), while those sources stating that the ULF range has a higher frequency than ELF range are primarily from the United States.

Micropulsations or geomagnetic pulsations are responses to changes in the magnetosphere. The magnetosphere is a cavity in the solar wind, which is the result of the geomagnetic field (earth's magnetic field) impeding the direct entry of the ionized gas (plasma) of the solar wind into the cavity. Micropulsations were first observed and published by Balfour Steward (also spelled Stewart) in 1861. He described pulsations with frequencies ranging from 3 mHz to 30 mHz. Today, geomagnetic pulsations cover the frequency range from 1 mHz to 1 Hz. Pulsations are divided into two classes, continuous and irregular, each of which are further divided according to the period of the pulsations.

Some research has found that the variations in the geomagnetic field strength (which micropulsations are a response to) can affect one's health, especially cardiovascular health. Dr. Eliyahu Stoupel published his results in the Bio-Electro-Magnetics Institute (vol. 1, no. 1) in the spring of 1989. Research into micropulsations and their resonances may also be applied to space meteorology, field-line resonances (FLRs) in the magnetospheres of other planets, and other geomagnetic activity (GMA), including geomagnetic storms and flares.

Elizabeth T. Wong -- 2001