Asymmetric V shaped streaks recorded on board DEMETER, above powerful thunderstorms

Both symmetric and asymmetric forms of V-shaped streaks observed on board DEMETER satellite are reported. They are associated with intense and numerous 0+ whistlers generated above high active thunderstorms regions. To understand the origin of the different spectral forms, a systematic survey is performed over 5 years of VLF-data. Asymmetric events are more frequently observed for high latitude regions. The importance of the magnetic field orientation on the spectral form observed is pointed out and confirmed by: - A propagation model based on cold plasma properties. - An event study where positions of the lightnings strokes were precisely known.