Preliminary results from the Sprites94 Aircraft Campaign: 1. Red sprites

Abstract

The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed “sprites” after their elusive nature, are luminous structures of brief (< 16 ms) duration with a red main body that typically spans the altitude range 50–90 km, and possessing lateral dimensions of 5–30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, “blue jets,” are described in a companion paper [Wescott et al., this issue].

Optical characteristics of red sprites produced by runaway air breakdown

“…To produce considerable ionization at lower altitude (higher than 55 km) the higher altitude of the discharge (z = 20 km) was needed. However, observations [Sentman et al, 1995] show that blue tendrils of red sprites extend downward to 35 kin, or even lower.…”

“…The ground-based observations [Winckter et at., 1996; Rairden and Mende, 1995; Hampton et at., 1996; Lyons, 1996] show similar results, and provide additional information on the spatial and temporal structure of sprites [Winckter et at., 1996; Rairden and Mende, 1995], and on identification of sprite locations over mesoscale convective systems [Lyons, 1996]. One difference between high-altitude and ground-based observations is that blue tendrils, observed from aircraft [Sentman et at., 1995], have rarely been seen from the ground. The photometer observations [Winckler et al, 1996] show that the typical duration of a sprite is several milliseconds but can extend to several hundred milliseconds.…”

“…Aircraft-based observations obtained with low-light-level cameras [Sentman et at., 1995] show that sprites are predominantly red in color with faint blue tendrils, which extend downward to altitudes of 40 km; that the duration of a single sprite is less than 17 ms, that their maximum brightness is about 600 kR, and that their estimated total optical energy is about 1-5 kJ per event. The ground-based observations [Winckter et at., 1996; Rairden and Mende, 1995; Hampton et at., 1996; Lyons, 1996] show similar results, and provide additional information on the spatial and temporal structure of sprites [Winckter et at., 1996; Rairden and Mende, 1995], and on identification of sprite locations over mesoscale convective systems [Lyons, 1996].…”

Derivation of a merging condition for two interacting streamers in air

“…are observed in sprites: large-scale discharges which appear at low pressure in the altitude range of about 40 to 90 km above large thunderstorms [2,3]. Streamers often form branches.…”

The 762 nm emissions of sprites

“…[2] A sprite is one of several types of transient luminous events (TLEs) induced in the upper atmosphere by thunderstorms, and it usually occurs in the altitude range of 40-90 km [Sentman et al, 1995]. Telescopic images of sprites show the existence of narrow filamentary plasma structures in sprites, called streamers.…”