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| Titel |
Acoustic and infrasonic measurements of thunder during the HyMeX SOP1 campaign in 2012 and comparison with new modeling results |
| VerfasserIn |
Arthur Lacroix, Thomas Farges, Regis Marchiano, François Coulouvrat |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142897
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| Publikation (Nr.) |
 EGU/EGU2017-6575.pdf |
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| Zusammenfassung |
| Thunder is composed of complex acoustic waves with a rich infrasonic and audible frequency
spectrum. This complexity depends both on the source and the propagation of the wave to the
observer. However there is no mutual agreement on the link between the observed spectral
content and the generation mechanisms.
The objective of this study is to provide new experimental results and their comparison to
theoretical investigations. An acoustic station was deployed in Fall 2012 during the first
Special Operation Period of the HyMeX project in South of France. This station
was composed of 4 microphones arranged in a triangle of 50-m side with one of
them at the center and 4 microbarometers arranged in a triangle of 500-m side with
one of them co-localized with the central microphone (Defer et al., 2015). During
more than 2 months, about ten thunderstorms occurred over the station producing
many cloud-to-ground and intracloud flashes. Several thousands of acoustic signals
and electromagnetic detections from research and operational lightning location
networks were recorded. Our database contains a sufficient number of flashes close to
the source (< 1km) to minimize propagation effects and to focus on the source
effects.
The 3D reconstruction of the acoustical sources using the acoustic signals (from 1 to 40
Hz) shows that these signals are mainly localized inside the lightning channel joining the
cloud to the ground and produced during the return stroke phase of the flashes (Gallin et al.,
2016). These observations are compatible with a source mechanism due to the thermal
expansion associated to the sudden heating of the air in the lightning channel. An original
model inspired by Few’s string pearl theory (Few, 1969) has been developed. It shows that the
tortuous channel geometry explains at least partly the low frequency content of observed
thunder spectrum. |
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