Sprite initiation altitude measured by triangulation

Abstract

[1] High time resolution (10,000 frames per second) images of sprites combined with multistation concurrent video recordings have provided data for triangulation of the altitude of the initial sprite onset. The high-speed images were obtained from the Langmuir Laboratory, New Mexico, during summer campaigns in 2007 and 2008 with video observations from sites at Portales, New Mexico, and Las Vegas, New Mexico. Sprites start with one or more downward-propagating streamer heads. The triangulated onset altitudes of this initial downward streamer vary between 66 and 89 km. In some sprites the downward streamers are followed a little later by upward-propagating streamers. The upward streamers start from a lower altitude and existing luminous sprite structures and their triangulated altitudes vary from 64 to 78 km. The downward streamers create C sprite characteristics, while the upward streamers form the broad diffuse tops of carrot sprites. In the sprites analyzed the higher onset altitudes for the downward-propagating initial streamers were associated with C sprites and the lower with carrot sprites, but our larger data set indicates that this is not generally the case. It appears that the dominant sprite types vary from year to year, indicating that some longer-lasting environmental parameter, such as mesospheric conductivity and composition or thunderstorm cloud dynamics, may play an important role in determining the types of sprites observed.

Sprite possibly produced by two distinct positive cloud-to-ground lightning flashes

“…4b may be the upward streamers that lead to the observed carrot sprites, in good agreement with the results reported by Stenbaek-Nielsen et al (2010) in which downward streamers create C type sprites (namely, columniform sprites, characterized by bright vertical columns in video imagery), while the upward streamers form the broad diffuse tops of carrot sprites. It should be noted that the bottom and top altitudes of sprites in this study may be underestimated to some extent because of clouds in the camera field of view.…”

“…4b) shows that it mainly developed upward. High-speed images reported by Stenbaek-Nielsen et al (2010) showed that sprites start with downward-propagating streamer heads at altitudes varying between 66 and 89 km, and in some cases the downward streamers are followed later by upward streamers starting from a lower altitude varying from 64 -78 km.…”

Sprite streamer initiation from natural mesospheric structures

“…This conclusion is also consistent with the result from a recent analysis of high-speed images obtained with one of the most sensitive cameras currently in use in sprite observation. For streamers emerging out of a dark background, the analysis has indicated that the first detected streamer heads likely have already propagated a few kilometres 29 .…”

“…In addition, only the bottom half simulation region is shown for the optical emissions, because there are no visible emissions above. The intensity of the glow at 6 ms before streamer initiation is much weaker than the streamer head at 6.55 ms that has propagated more than 1 km distance, which is likely to be the first streamer head detected by intensified, high-speed cameras 29 . The intensity of the preceding glow is therefore below the detection limit of the current sprite observation systems, and this streamer will appear to emerge from a dark background.…”

“…Those studies also show that about half of the observed sprites appear after a more than 10 ms delay from the causative CGs 27 , and they are initiated around 70-km altitude, lower than that of prompt sprites [27][28][29] . The long-continuing current of the parent lightning can maintain a moderate electric field at the sprite initiation altitude, and sometimes sprite initiation occurs during a 5-20 ms rise of the current 27 .…”