Identification of sprites and elves with intensified video and broadband array photometry

Confusion in the interpretation of standard-speed video observations of opt ical flashes above intense cloud-to-ground lightning discharges has persist ed for a number of years. New high-speed (3000 frames per second) image-int ensified video recordings are used along with theoretical modeling to eluci date the optical signatures of elves and sprites. In particular, a brief di ffuse flash sometimes observed to accompany or precede more structured spri tes in standard-speed video is shown to be a normal. component of sprite el ectrical breakdown and to be due entirely to the quasi-electrostatic thunde rcloud field (sprites), rather than the lightning electromagnetic pulse (el ves). These "sprite halos" are expected to be produced by large charge mome nt changes occurring over relatively short timescales (similar to1 ms), in accordance with their altitude extent of similar to 70 to 85 km. The relati vely short duration of this upper, diffuse component of sprites makes it di fficult to detect and to discriminate from elves and Rayleigh-scattered lig ht using normal-speed video systems. Modeled photometric array signatures o f elves and sprites are contrasted and shown to be consistent with observat ions. Ionization in the diffuse portion of sprites may be a cause of VLF sc attering phenomena known as early/fast VLF events.