Dawn chorus (electromagnetic)

The electromagnetic dawn chorus is a phenomenon that occurs most often at or shortly after dawn local time. With the proper radio equipment, dawn chorus can be converted to sounds that resemble birds' dawn chorus (by coincidence).

VLF spectrogram of electromagnetic chorus, as received by the Stanford University VLF group's wave receiver at Palmer Station, Antarctica. The chorus can be seen between 1000 Hz and 3000 Hz, sandwiched between components of sferics

The electromagnetic dawn chorus is believed to be generated by a Doppler-shifted cyclotron interaction between anisotropic distributions of energetic (> 40 keV) electrons and ambient background VLF noise. These energetic electrons are generally injected into the inner magnetosphere at the onset of the substorm expansion phase.[1][2] Dawn choruses occur more frequently during magnetic storms.

This phenomenon also occurs during aurorae, when it is termed an auroral chorus.

See also

Notes
  1. Nunn, D.; Omura, Y.; Matsumoto, H.; Nagano, I.; Yagitani, S. (1997). "The numerical simulation of VLF chorus and discrete emissions observed on the Geotail satellite using a Vlasov code" (PDF). J. Geophys. Res. 102: 27083–27098. Bibcode:1997JGR...10227083N. doi:10.1029/97JA02518.
  2. Trakhtengerts, V. Y. (1999). "A generation mechanism for chorus emission". Ann. Geophys. 17: 95–100. Bibcode:1999AnGeo..17...95T. doi:10.1007/s00585-999-0095-4.

Further reading
  • Robert A. Helliwell (2006) [1965]. Whistlers and Related Ionospheric Phenomena. Dover Publications, Inc. ISBN 0-486-44572-0.
  • Romero, R. (2008). Radio Nature. Potters Bar: Radio Society of Great Britain. pp. 39–40. ISBN 978-1-905086-38-2.
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