Observation and Analysis of Very Large and Luminous Sprites

Sprites are Transient Luminous Events (TLEs) consisting of streamer discharges, that develop at the base of the ionosphere and move rapidly downward, in response to a strong transient electrostatic field. According to the structure and the density of the streamers, they appear in various shapes that classifies them in several types, e.g., column, carrot, jellyfish, and angel. A large number of sprite observations have been made for several years with low-light video cameras located in southern France, especially at Pic du Midi (2877 m) in the Pyrénées mountain range and at the Albion Plateau in Rustrel (1000 m). This study focuses on the most luminous of these events to determine some of their characteristics and the context in which they are produced. Thus, we analyse the video imagery, the lightning processes at the origin of the sprite events, the characteristics of the thunderstorms that produce them. Such very bright sprites occur above thunderstorms at any period of the year. All cases of sprite events are associated with a halo weakly luminous. They are produced with a very short delay after strong positive cloud-to-ground strokes, with peak currents of 150 kA in average and huge iCMC values that can reach close to 2000 C km. Several characteristics of the thundercloud, as the lightning activity, the cloud top temperature, the size and the structure, will be considered in order to better understand the conditions of production of such sprite events.