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Whistler (radio)

VLF spectrogram of an electromagnetic whistler wave, as received by the Stanford University VLF group's wave receiver at Palmer Station, Antarctica.

A whistler is a very low frequency (VLF) electromagnetic (radio) wave generated by lightning.[1] Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, with maximum frequencies usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies, and can be converted to audio using a suitable receiver. They are produced by lightning strikes (mostly intracloud and return-path) where the impulse travels along the Earth's magnetic field lines from one hemisphere to the other. They undergo dispersion of several kHz due to the slower velocity of the lower frequencies through the plasma environments of the ionosphere and magnetosphere. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.

Voyager 1 and 2 spacecraft detected whistler-like activity in the vicinity of Jupiter known as "Jovian Whistlers",[2] supporting the visual observations of lightning made by Voyager 1.[3]

Whistlers have been detected in the Earth's magnetosheath, where they are often called “lion roars” due to their frequencies of tens to hundreds of Hz.[4]

  1. ^ Robert A. Helliwell (2006). Whistlers and Related Ionospheric Phenomena. Dover Publications, Inc. ISBN 978-0-486-44572-4. Originally published by Stanford University Press, Stanford, California (1965).
  2. ^ Hobara, Y.; Kanemaru, S.; Hayakawa, M.; Gurnett, D. A. (1997). "On estimating the amplitude of Jovian whistlers observed by Voyager 1 and implications concerning lightning". Journal of Geophysical Research: Space Physics. 102 (A4): 7115–7125. Bibcode:1997JGR...102.7115H. doi:10.1029/96JA03996. ISSN 2156-2202.
  3. ^ Aplin, Karen L.; Fischer, Georg (February 2017). "Lightning detection in planetary atmospheres". Weather. 72 (2): 46–50. arXiv:1606.03285. Bibcode:2017Wthr...72...46A. doi:10.1002/wea.2817. ISSN 0043-1656.
  4. ^ Baumjohann, W.; Treumann, R. A.; Georgescu, E.; Haerendel, G.; Fornacon, K.-H.; Auster, U. (1999-12-31). "Waveform and packet structure of lion roars". Annales Geophysicae. 17 (12): 1528–1534. Bibcode:1999AnGeo..17.1528B. doi:10.1007/s00585-999-1528-9. ISSN 0992-7689. S2CID 11493967.

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