Very low frequency sferic bursts, sprites, and their association with lightning activity

Recent observations have revealed the occurrence of burst‐like VLF activity, lasting from tens of milliseconds up to a few seconds, associated with the onset of many sprites. These “sferic bursts” are thought to be due to the horizontal in‐cloud component of lightning activity, since they have been observed to propagate only short distances (a few hundred kilometers) in the Earth‐ionosphere waveguide and are generally not reported by lightning detection networks. The possible involvement of in‐cloud lightning in sprite production has been previously suggested on the basis of the observed long delays and spatial displacement between causative cloud‐to‐ground (CG) discharges and sprite events. In this work, we investigate the association between sprites and sferic bursts using VLF data and a large set of sprite observations between 1995 and 2000. We compare the occurrence of sferic bursts in association with sprites for thousands of observations through many different dates and thunderstorms. Results indicate that sprite‐causative CGs are more commonly found in association with bursts of sferic activity than those CG discharges without sprites and that, furthermore, the distribution of sferic burst VLF energy is significantly higher for sprite‐associated events. We further investigate the source of these bursts by comparing VLF data to Lightning Mapping Array (LMA) data of VHF pulses due to lightning. Such comparisons show that most sferic burst events can be explained as radiation from the horizonal in‐cloud components of +CG lightning, as detected by the LMA.