Hiss (electromagnetic)

Electromagnetic hiss is a naturally occurring Extremely Low Frequency/Very Low Frequency electromagnetic wave (i.e., 300 Hz – 10 kHz) that is generated in the plasma of either the Earth's ionosphere or magnetosphere. Its name is derived from its incoherent, structureless spectral properties which, when played through an audio system, sound like white noise (hence the onomatopoetic name, "hiss").
Varieties.
Hiss may be observed in any of several varieties depending on local time and L-shell of the observer:
Generation mechanisms.
There are several proposed generation mechanisms for plasmaspheric hiss in particular, including: