Multi-instrumental analysis of large sprite events and of their producing storm in southwestern France

During the night of 01-02 September, 2009, several TLEs including 3 halos and 16 distinct sprites were observed above a storm in north-western Mediterranean Sea with a camera at Pic du Midi (42.93° N, 0.14° E, 2877 m). Some of the sprites were especially large with vertical and horizontal extension estimated at about 70 km and 80 km, respectively. The TLE sequence lasted about one hour during a storm which developed 9 hours earlier over northern Spain in a very unstable atmosphere (CAPE at about 2000 J kg-1). The storm was characterized by a very circular shape and a size of about 250×250 km2 (cloud top temperature lower than -30°C) when the TLEs were produced (0209-0307 UT). The cloud to ground (CG) flash rate was large (45 min-1) one hour before the first TLE was detected and very low (< 5 min-1) during the TLE production. Over the 16 sprite events, 14 parent flashes were identified and their average peak current was 87 kA, while the associated charge moment changes which could be determined, ranged from 424 to 2088 C km. Most parent flashes were clearly located in the stratiform area of the storm and were into line with the lines of sight of the TLEs. For some parent flashes which were located closer to the convective area, the TLEs lines of sight were slightly shifted and remained over the stratiform area. Different ELF/LF radiations produced during the luminous events have been analyzed. A specific signature with long duration signal (> 5 ms) was observed for the electric field in ELF range in the cases of the very large sprites. Data from a VLF receiver shows the association between large sprites and early VLF signal perturbations.