Estimation of Sprite Streamers Altitude Based on the Spectrophotometric Observations

Sprites are transient luminous events (TLEs) that result from the electrostatic coupling between thunderstorm charges following a positive cloud-to-ground lightning (+CG) and the lower ionosphere. These fine-structured objects are composed of filamentary streamer discharges propagating in the D-region of the ionosphere and the mesosphere. Optical emissions from sprite streamers are used to estimate peak electric fields and electron energies [e.g., Kuo et al., GRL, 32, L19103, 2005 ; Adachi et al., GRL, 33, L17803, 2006]. It has been shown that significant correction factors need to be used to account for the spatial shift between distributions of optical emissions in streamers and peak electric fields in their heads [Celestin and Pasko, GRL, 37, L07804, 2010]. The latter study involved the excited species {N}₂(C³Π_u and {N}₂⁺(B^{2} Σ_u+), whose populations are considered to be in steady state. The species {N}₂(C³Π _{u) and {N}₂⁺(B^{2} Σ_u+) are responsible for the second positive ({2PN}₂) and first negative ({1NN}₂⁺) bands systems of {N}₂ and {N}₂⁺, respectively. In this work, we show how this technique can be extended to non-steady state optical emissions, such as those produced by {N}₂(a¹ Π_{g) and {N}₂(B³Π_{g) in the form of Lyman-Birge-Hopefield ({LBH}) and first positive ({1PN}₂) bands systems, respectively. Additionally, we simulate numerically downward propagating sprite streamers and their optical emissions for the following bands systems: {1PN}₂, {2PN}₂, {LBH}, and {1NN}₂⁺, and expose the developed spectrophotometric technique to infer physical properties such as the altitude and the velocity of sprite streamers [Ihaddadene and Celestin, submitted for publication to JGR, 2016]. This study particularly aims at improving analysis of observational results in nadir-viewing geometry of the space missions GLIMS (JAXA), ASIM (ESA), and TARANIS (CNES).