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SEE ALSO: Research Expedition to Mongolia 1998
SEE ALSO: Global Electrophonic Fireball Survey
Video images of a meteor that produced an electrophonic sound.
You can download the movie here (the moment of electrophonic sound is marked with "E").
Meteors produce two types of sound---normal and anomalous
(electrophonic). The latter lack a time delay between the visual
appearance of the meteor and audible detection on the ground, an
apparent contradiction recognized more than 300 years ago. These
sounds most probably result from corona discharge and
vibration of objects due to a local quasi-electrostatic (ELF/VLF
frequency range) enhancement of the electric field (Vinkovic
et al. 2002, WGN-JIMO, 30, 244). However, the physical mechanism of
electric field amplification by a meteor is still a complete mystery.
In 1998 I helped organize the Croatian Physical Society expedition to Mongolia
to detect the ELF/VLF radio emission and electrophonic sounds from the Leonid
meteor shower. We succeeded in obtaining the first ever instrumental recording
of meteor electrophonic sounds (Zgrablic et al, JGR
2002, 107(A7); see also
fizika.org/ilwcro/results). Post-analysis
shows that all the existing theories fail to explain the observations. The
results represent a milestone in this field of study. I am currently
coordinating the Global Electrophonic Fireball Survey
(www.gefsproject.org), a project that
studies the phenomenon and collects witness reports.
Zgrablic, G., Vinkovic, D., Gradecak, S., Kovacic, D., Biliskov,
N., Grbac, N., Andreic, Z, & Garaj, S. 2002, Journal of
Geophysical Research (Space Physics), 107, 11
(ADS,
PDF)
Garaj, S., Vinkovic,
D., Zgrablic, G., Kovacic, D., Gradecak, S., Biliskov, N., Grbac, N., & Andreic, Z. 1999, Fizika A, 8, 91
(ADS,
PDF)
Vinkovic, D., Garaj, S., Lim, P.L., Kovacic, D., Zgrablic, G., &
Andreic, Z., 2002, WGN, Journal of the International Meteor
Organization, 30, 244 (ADS, PDF)
Vinkovic, D., Andreic,
Z., Garaj, S., Kovacic, D., Mladinov, M., & Zgrablic, G. 2000, WGN,
Journal of the International Meteor Organization, 28, 48 (ADS, PDF)
Spectral distribution (sound amplitude .vs. sound frequency .vs. time) of
two electrophonic sounds detected during the expedition to Mongolia in
1998. Each electrophonic sound was detected on two separate
microphones. Left column: the sound from the -6.5 m
fireball; Right column: the sound from the -12 m
fireball; Color: relative sound amplitude in dB.
See
Zgrablic et al. 2002, JGR (Space Physics), 107, 11
( PDF) for more information.
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