HF-VHF Electromagnetic Emissions From Collisions of Sprite Streamers

Abstract

Sprites are complex transient plasma discharges that consist of many plasma filaments named streamers. They are produced high above thunderstorms. Sprites are known to produce electromagnetic radiation observed typically in the extremely low (ELF), ultra low (ULF), to as high as medium frequency (MF) radio bands. Recent research work showed that head-on streamer collisions lead to a reinforcement of the electric field over a short time scale, typically a few picoseconds at ground-level. The use of the similarity laws leads to a corresponding time scale on the order of a fraction of a microsecond at 50 km altitude, which opens the eventuality for HF-VHF emissions from sprites. In this study, using a multifluid streamer model paired with an antenna model assimilating the streamer as a straight segment. We simulate head-on collision between two streamers with opposite polarities in order to evaluate their electromagnetic emissions. We report numerical prediction of the electromagnetic signature for 50, 60, 70, and 80 km altitudes. The magnetic field radiated varies over four orders of magnitude, between less than 0.1 fT and 7 pT. Comparing the spectral density from the head-on collision between two streamers with IME-HF (TARANIS), ICE (DEMETER), and FORTE RF payload, we find that IME-HF and ICE could detect these signatures. We compare these results with sensitive ground-based instruments like the radiotelescope NenuFAR, and show that detections of such events might be possible with this type of fast and sensitive radiotelescopes.