Dawn chorus (electromagnetic)

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 an unexplained phenomenon that occurs most often at sunrise or shortly after, that (with the proper radio equipment) resembles the sound of the birds' dawn chorus. 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.^[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

• Auroral chorus
• Hiss (electromagnetic)
• Whistler (radio)

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". J. Geophys. Res. 102: 27083–27098. doi:10.1029/97JA02518. 
2. ^ Trakhtengerts, V. Y. (1999). "A generation mechanism for chorus emission". Ann. Geophys. 17: 95–100. 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 9781-9050-8638-2. 

External links

• Stephen P. McGreevy's ground-based ELF-VLF recordings
• Natural VLF Radio - Sounds of Space Weather
• Space-Weather Sounds - the Mysterious and Beautiful Natural Radio Phenomena of Earth