Dawn_chorus_(electromagnetic)

Dawn chorus (electromagnetic)

Dawn chorus (electromagnetic)

Electromagnetic wave phenomenon

The electromagnetic dawn chorus is a phenomenon that occurs most often at or shortly after dawn local time. It 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.

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

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

With the proper radio equipment, dawn chorus can (by coincidence) be converted to sounds that resemble birds' dawn chorus.

See also

Notes

  1. [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 (A12): 27083–27098. Bibcode:1997JGR...10227083N. doi:10.1029/97JA02518.
  2. [2]
    Trakhtengerts, V. Y. (1999). "A generation mechanism for chorus emission". Ann. Geophys. 17 (1): 95–100. Bibcode:1999AnGeo..17...95T. doi:10.1007/s00585-999-0095-4.

Further reading

Look up dawn chorus in Wiktionary, the free dictionary.
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