HR: 1340h
AN: AE23A-0898    [Abstracts]
TI: Sprite and Lightning Infrasound Measurements during the 2005 Eurosprite Campaign
AU: * Farges, T
EM: thomas.farges@cea.fr
AF: CEA, BP 12, Bruyeres le Chatel, 91680, France
AU: Blanc, E
EM: elisabeth.blanc@cea.fr
AF: CEA, BP 12, Bruyeres le Chatel, 91680, France
AU: Herry, P
EM: pascal.herry@cea.fr
AF: CEA, BP 12, Bruyeres le Chatel, 91680, France
AU: Flavin, V
EM: valerie.flavin@cea.fr
AF: CEA, BP 12, Bruyeres le Chatel, 91680, France
AU: Neubert, T
EM: neubert@space.dtu.dk
AF: DNSC, Juniane Maries Vej 30, Copenhagen, 2100, Denmark
AB: Liszka [2004] first assumed that infrasound have a specific signature in their spectrogram (a chirp) when a sprite occurs. During the Eurosprite 2003 campaign, Farges et al. [2005] correlated such kind of infrasound with camera observation of sprite. They used the data of the Flers infrasound station located in the North-West of France. The correlation between the time of an infrasound due to sprite and the sprite time is done by calculating the propagation time with a ray-tracing model. A clear relation between the infrasound duration and the sprite size has been found. For the Eurosprite 2005 campaign, in addition to the permanent infrasound station of Flers, a supplementary station has been set up in St Just at ~400 km southward away from Flers. The two main objectives for the infrasound campaign were: i) to measure the same sprite infrasound with two stations and to possibly locate it and ii) to evaluate the attenuation with distance of the infrasound produced by lightning. The expected result of this second objective was the confirmation that the chirp signature is due to the sprite alone and not to the sprite and its parent lightning. The conditions allowing the observation of sprites have been investigated. For instance, numerous infrasounds of sprites were detected during a large storm on September 26th. But the location of this sprite-producing storm (southward relatively to the two sensors and over the Mediterranean Sea) limited the capability to detect them with both stations and then to locate a sprite from joined infrasound measurements. Studies on the characteristics of infrasound of lightning have been done, particularly on September 10th, when a storm moved North-Eastward from the Bay of Biscay, passing just over the St Just station. At the same time, no lightning activity was recorded at less than 200 km away from Flers station. The amplitude of infrasound produced by lightning is higher than the noise only when lightning are located at distances lower than 50 km from the station. When lightning are close to station, the infrasound amplitude reach few Pa and a dynamic of 30 dB (in comparison to the noise level) is then found. Simultaneously, nothing has been detected in the Flers station data. These joined measurements show clearly that infrasound produced by lightning could be only measured at short distance from the source. The chirp signature is then definitely a property of sprite infrasound. Spectrum of isolated lightning is also examined. A flat response between 0.3 and 1 Hz is found when the lightning distance is less than 20 km from the station. As Liszka shown at the previous AGU Fall meeting [2006], we found also some infrasound which can document the measurement of infrasound due to intracloud discharge. At last, from the infrasound signals detected at St Just, we try to evaluate the charge amount discharged during a return-stroke as it was theoretically assumed by Dessler [1973] and Few [1985].
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting