Comparison of results from sprite streamer modeling with spectrophotometric measurements by ISUAL instrument on FORMOSAT-2 satellite

Three intensity ratios of the second positive band system of N₂ to N₂ LBH band system, the first negative band system of N₂⁺, and the first positive band system of N₂ are obtained separately from sprite streamer modeling and from measurements by ISUAL instrument on FORMOSAT-2 satellite. The direct comparison between the obtained ratios indicates that in order to explain the ISUAL spectrophotometric data the maximum field driving the emissions of an observed sprite event must be greater than three times of the conventional breakdown threshold field. These findings are consistent with an assumption that most of the observed sprite emissions during initial sprite development originate from localized high field regions associated with tips of sprite streamers.