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Electromagnetic
In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...
hiss is a naturally occurring Extremely Low Frequency/Very Low Frequency
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave ...
electromagnetic wave
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ...
(i.e., 300 Hz – 10 kHz) that is generated in the plasma of either the Earth's ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
or magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior Dynamo ...
. Its name is derived from its incoherent, structureless spectral properties which, when played through an audio system, sound like white noise
In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. The term is used with this or similar meanings in many scientific and technical disciplines, i ...
(hence the onomatopoetic name, "hiss").
Varieties
Hiss may be observed in any of several varieties depending on local time andL-shell
The L-shell, L-value, or McIlwain L-parameter (after Carl E. McIlwain) is a parameter describing a particular set of planetary magnetic field lines. Colloquially, L-value often describes the set of magnetic field lines which cross the Earth's ...
of the observer:
* ''Plasmaspheric hiss'' is generally observed within the plasmasphere, peaking in frequency slightly below ~1 kHz and rarely exceeding 3 kHz.
* ''Exo-hiss'' and ''ELF hiss'' are two varieties of hiss observed outside of the plasmasphere, both having a spectrum similar to that of plasmaspheric hiss.
* ''Midlatitude hiss'' is generally observed outside of the plasmasphere and tends to have frequencies between 2 and 10 kHz.
* ''Auroral hiss'' is observed in the auroral zones of the Earth and can extend up to several hundred kHz.
Generation mechanisms
There are several proposed generation mechanisms for plasmaspheric hiss in particular, including: * Generation from discrete chorus emissions * Generation via electromagnetic impulses from terrestriallightning
Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...
, specifically via lightning-generated whistlers
* Generation through coherent nonlinear interaction with energetic electrons near the equatorial plasmasphere
See also
* Dawn chorus (electromagnetic) *Whistler (radio)
A whistler is a very low frequency (VLF) electromagnetic (radio) wave generated by lightning. Originally published by Stanford University Press, Stanford, California (1965). Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, wi ...
References
{{DEFAULTSORT:Hiss (Electromagnetic) Electrical phenomena Geomagnetism