Electric fields and electron energies inferred from the ISUAL recorded sprites

Abstract

[1] Electron energies and the strength of electric fields in sprites are deduced for five selected events, which were recorded by the space-borne instrument called ISUAL (Imager of Sprites and Upper Atmospheric Lightning; a payload on the FORMOSAT-2 satellite). From the derived peak intensity ratios of spectrophotometer channel 2 (centered at 337 nm) and channel 3 (centered at 391.4 nm) of these sprites, the average and characteristic electron energies were found to be in the range of 6.2-9.2 eV and 4.5-6.5 eV, respectively. The estimated E/N at 40-60 km is 243-443 Td and the strength of the electric field is 2.1-3.7 times that of the atmosphere breakdown E-field at these altitudes. The inferred electron energies and the strength of electric fields are about two times higher than those inferred from ground campaigns. However, they are consistent with the prediction of the sprite streamer model.

Vibrational kinetics of air plasmas induced by sprites

“…Later on, the work by Morrill et al [2002] showed that the characteristic electron energies at altitudes below 55 km was ∼2.2 eV, while they reached a minimum of ∼1.75 eV at 60 km. More recent measurements (100 ms average) by the ISUAL instrument on board the FORMOSAT-2 satellite [Kuo et al, 2005] have shown that the average electron energies in the luminous regions of sprites are between 6.2 eV and 9.2 eV. This finding suggests that, in a first stage, electrons are capable of generating a considerable degree of excitation and ionization in the low-temperature air plasmas confined within the streamer tips and, consequently, an important number of atmospheric species can become chemically active through (initially) electron-driven reactions.…”

“…The upper limit of the E/N values reported [Kuo et al, 2005] is in agreement with the electric field magnitudes (>3 E k /N) predicted in recent models of sprite streamers [Liu et al, 2006]. However, a more recent work [Adachi et al, 2008] using the blue to red (B/R) emission ratios observed by the dual-color array photometer (AP) of the ISUAL instrument indicates that the peak values of the reduced electric fields are 59-149 Td in the upper-diffuse region of sprites (above around 75 km) and 98-380 Td in the sprite lower-streamer-like region (below around 75 km).…”

“…[7] The reduced electric field E/N underlying the brightest sprite optical emissions has been recently estimated with the six-color spectrophotometer (SP) of the ISUAL instrument by studying 2PN 2 /1NN 2 + ratios of several sprites observed between an altitude of 40 and 60 km and the reported E/N fields range between 243 Td and 443 Td (2.1-3.7 E k /N, where E k /N = 128 Td is the atmosphere breakdown reduced electric field and N is the gas density) [Kuo et al, 2005]. The upper limit of the E/N values reported [Kuo et al, 2005] is in agreement with the electric field magnitudes (>3 E k /N) predicted in recent models of sprite streamers [Liu et al, 2006].…”

The 762 nm emissions of sprites

“…A streamer can initiate from a single electron avalanche at sprite altitudes and develop into a propagating ionization wave driven by a weak background electric field [Liu and Pasko, 2004, and references therein]. The inferred electric field derived from spectroscopic analysis [Kuo et al, 2005] or streamer modeling [Liu and Pasko, 2005;Liu et al, 2006] indicates a high electric field in the streamer head, which can trigger a series of chemical reactions. Sentman et al [2008] developed a plasma chemical streamer model (hereinafter referred to as S08) to quantify the local chemical effects for a passing sprite streamer at 70 km altitude.…”

ISUAL Imager and far-ultraviolet spectrophotometer degradation

“…The far-ultraviolet (FUV) emissions emitted by transient luminous events (TLEs) originated in the Lyman-Birge-Hopfield (LBH) band of nitrogen molecule N 2 . From the ISUAL data analyses, it is known that elves Kuo et al 2007Kuo et al , 2008Chang et al 2010), halos Kuo et al 2008), sprites (Kuo et al 2005Liu and Pasko 2005;Liu et al 2006), and gigantic jets (Kuo et al , 2009Chou et al 2010) are accompanied by FUV emissions. However, blue jets without the FUV emission were also reported (Chou et al 2010) as the longer life time of the N 2 LBH band upper state results in quenching at the lower altitudes.…”