Triangulated sprite initiation altitudes

In June/July 2008 high-speed sprite observations were made from the Langmuir Laboratory, NM, with concurrent video observations from two other sites in New Mexico, Portales and Las Vegas. The two outlying sites together with the observations at Langmuir provided data for locating the sprites geographically by triangulation, which, in turn, provide an altitude calibration of the high-speed images. High-speed observations (10,000 fps) from this and earlier campaigns have shown sprites to start with one or more downward propagating streamer heads. In the wake of the streamer head columnar luminosity forms creating the C-sprite signature easily recognizable in video recordings. In some sprite there are also upward propagating streamers. When they occur they occur later and their onset is from a lower altitude and from existing luminous sprite structure. The upward streamers form the diffuse higher altitude branches. In video recordings such sprites would be classified as carrot sprites. Preliminary analysis of the 2008 data show the altitude of the sprite onset, i.e. the altitude of the first detection of the initial downward streamer, vary from 66 km to 88 km. The higher onset altitudes appear to be associated primarily with C-sprite events.