Identification of infrasound produced by sprites during the Sprite2003 campaign

Abstract

During the summer of 2003, complementary measurements were taken in Europe during the Sprite2003 campaign to study sprites and associated processes. On July 21, 28 sprites observed by light‐sensitive optical cameras located at the Observatoire du Pic du Midi in the Pyrenees mountains were found to correlate with chirp‐like signals of several tenth to few minutes duration, measured by an infrasound station at Flers about 400 km from the thunderstorm. The sprite activity identified by the infrasound signature continued past sunrise into the daytime when optical systems cannot be used, documenting the occurrence of daytime sprites. Using an acoustic wave propagation model, the observed propagation delays, frequency dispersion, and duration of the infrasound bursts are found to be consistent with source altitudes at 60–80 km with horizontal dimensions equal to the optical width of the sprites. The chirp‐like dispersion is a result of the propagation properties in the earth‐thermosphere waveguide.

Recent Results from Studies of Electric Discharges in the Mesosphere

“…A model study shows that a vertically extended cylindrical volume with a radial dimension of the order of several tens of meters placed in the mesosphere and heated by 5°K, consistent with previous analyses ( Pasko et al 1998), is sufficient to explain the amplitude of infrasound from a sprite (Pasko and Snively 2007). The result supports the ideas advanced by Farges et al (2005) that the chirp-shape can be explained During the night of 21 July 2003, infrasound chirp signals were detected after the cameras were shut down because of the approaching dawn . Several chirp-shaped infrasound waves were measured from 3:50 to 6:00 UT.…”

Lightning-associated VLF perturbations observed at low latitude: Occurrence and scattering characteristics

“…Stanley et al (2000) detected 3 separate daytime sprites on 14 August, 1998, via a unique sprite ELF signature recorded at a site in New Mexico, following exceptionally large lightning discharges. Farges et al (2005) were the rst to measure infrasound waves emitted from sprites past sunrise and onwards into the daytime, and suggested the occurrence of daytime sprites. Given that the signatures of daytime sprites (ELF and infrasound) have been detected by researchers, there is a possibility that daytime early VLF events reported here were associated with daytime sprites.…”

Seeking sprite‐induced signatures in remotely sensed middle atmosphere NO2

“…Moreover, reference observations of sprites are from nighttime optical images obtained during field campaigns [e.g., Arnone et al, 2008] of limited extent in time and space. The usability of electromagnetic measurements [e.g., Rodger, 2003] or infrasound signatures [Farges et al, 2005] associated with sprites is as yet uncertain. The best proxy for sprite activity is thus the causative tropospheric +CGs which are globally detected.…”