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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 8
Ann. Geophys., 24, 2179–2189, 2006
https://doi.org/10.5194/angeo-24-2179-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 2179–2189, 2006
https://doi.org/10.5194/angeo-24-2179-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  13 Sep 2006

13 Sep 2006

Early VLF perturbations observed in association with elves

Á. Mika1, C. Haldoupis1, T. Neubert2, H. T. Su3, R. R. Hsu3, R. J. Steiner1, and R. A. Marshall4 Á. Mika et al.
  • 1Department of Physics, University of Crete, Heraklion, Greece
  • 2Danish National Space Center, Copenhagen, Denmark
  • 3Department of Physics, National Cheng Kung University, Tainan, Taiwan
  • 4Space, Telecommunications, and Radioscience Laboratory, Stanford University, Stanford, USA

Abstract. VLF remote sensing is used to detect lower-ionospheric electron density changes associated with a certain type of transient luminous events known as elves. Both ground- and satellite-based observations of elves are analysed in relation to VLF data acquired at various receiver sites in Europe, the United States and Antarctica. Ground-based observations were performed during the EuroSprite2003 campaign, when five elves were captured by low-light cameras located in the Pyrenees. Analysis of VLF recordings from Crete shows early VLF perturbations accompanying all of the elves. A large dataset consisting of elves captured by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) payload on Taiwan's FORMOSAT-2 satellite over Europe and North America has also been analysed. Early/fast VLF perturbations were found to accompany some of the elves observed over Europe. However, no VLF perturbations were detected in relation to the elves observed by ISUAL over North America. The present analysis – based on the largest database of optical elve observations used for VLF studies so far – constitutes evidence of processes initiated by the lightning EMP (electromagnetic pulse) causing electron density changes in the lower ionosphere in line with theoretical predictions. It also proves that sub-ionospheric electron density changes associated with elves can intrude to lower heights and thus perturb VLF transmissions. The possibility of VLF detection, however, depends on several factors, e.g., the distance of the elve from the receiver and the transmitter–receiver great circle path (GCP), the altitude of the ionised region and the characteristics of the VLF transmitter, as well as the EMP energy, which occasionally may be sufficient to cause optical emissions but not ionisation.

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