Elves: Lightning-induced transient luminous events in the lower ionosphere

Observations of optical phenomena at high altitude above thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca. Ridge Field Station (40 degrees 40' N, 104 degrees 56' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These new measurements indicate that diffuse optical flashes with a duration of < 1 ms and a horizontal scale of similar to 100-300 km occur al 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as elves to distinguish them from red sprites''. This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.