During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3-3000 Hz) and broadband very low frequency (VLF: 3-30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites. The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods. Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.
|Number of pages||13|
|Journal||Journal of Atmospheric and Solar-Terrestrial Physics|
|State||Published - Aug 2009|
Bibliographical noteFunding Information:
This research was partially supported by the Israel Science Foundation Grant #145/03, and the Tel-Aviv University Research Fund. We would like to thank the Wise Observatory in Mitzpe Ramon, and the Solar Energy Research Center at Sde Boker, for allowing us to use their facilities for the ELF and VLF measurements. We are grateful to Umran Inan of Stanford University for providing the Crete VLF receiver, and for his continuous support. The Eurosprite2005 campaign was conducted by the CAL research training network sponsored by the European Commission under the Contract HPRN-CT-2002-00216. The authors thank all the CAL members involved in the optical observations, and the Météorage Company for providing the lightning data.
- Schumann resonance