Listening to shower meteors with infrasound

Abstract

Observations of the Leonid and Perseid meteor showers over the last few years in Europe using multiple camera systems, including the European Fireball Camera Network, have shown several bright meteors (abs. magnitudes −8 to −16) passing nearby to the IMS infrasound array in Freyung, Germany (I26DE). Subsequent checks of I26DE data show that these meteors were also detected infrasonically. This combination of optical location of the meteor in flight and microbarometer array beamforming has provided an excellent opportunity to delimit the altitudes at which these infrasound signals are being generated. UKMO temperature and wind data from the UARS satellite has been combined with MSIS and HWM models to reconstruct the acoustic velocity conditions present during observations. Using the reconstructed conditions, geometric ray tracing indicates that the source altitudes lie between approximately 80 to 105 kilometers; array back-azimuths appear to confirm this conclusion. This is extraordinary since meteoroids of this size, at these altitudes in the atmosphere, are in the transitional region from free-molecular flow to continuum flow. With these observations there is now confirmed infrasound from three separate meteor showers; the Leonids, Geminids and Perseids, meaning that meteor shower infrasound is much more common than previously thought.