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

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Abstract
Confusion in the interpretation of standard‐speed video observations of optical flashes above intense cloud‐to‐ground lightning discharges has persisted for a number of years. New high‐speed (3000 frames per second) image‐intensified video recordings are used along with theoretical modeling to elucidate the optical signatures of elves and sprites. In particular, a brief diffuse flash sometimes observed to accompany or precede more structured sprites in standard‐speed video is shown to be a normal component of sprite electrical breakdown and to be due entirely to the quasi‐electrostatic thundercloud field (sprites), rather than the lightning electromagnetic pulse (elves). These “sprite halos” are expected to be produced by large charge moment changes occurring over relatively short timescales (∼1 ms), in accordance with their altitude extent of ∼70 to 85 km. The relatively short duration of this upper, diffuse component of sprites makes it difficult to detect and to discriminate from elves and Rayleigh‐scattered light using normal‐speed video systems. Modeled photometric array signatures of elves and sprites are contrasted and shown to be consistent with observations. Ionization in the diffuse portion of sprites may be a cause of VLF scattering phenomena known as early/fast VLF events.