Strong evidence for a conventional breakdown mechanism in sprite initiation will be presented in this dissertation. Chapter 2 presents a review of conventional breakdown in the form of electron avalanches and streamer processes. Profiles of conductivity and atmospheric number density are used to determine the altitudes and corresponding charge moment values of sprite initiation. These results are compared with previous estimates of the altitudes and charge moment thresholds required for sprite initiation. A uniformly charged disc model of the parent discharge is used to determine how the breakdown threshold depends on the horizontal extent and average height of charge removal in a discharge. This model is then used to assess the validity of the point dipole approximation for the measured sprite-producing discharge heights and extents presented in Chapter 3.
In Chapter 3, the 3D spatial and temporal development, broadband electric field, and VHF emissions of both sprite-producing and non-sprite-producing discharges are analyzed and compared. The data contains the first reported average height, charge, and current values for several sprite-producing discharges. These results are compared with previous measurements of negative and positive CG discharge parameters. The charge moments are also compared with previous ELF-based estimates of the sprite initiation threshold as well as with theoretical predictions. The plan locations of the sprites are compared with discharge development up to the time of the sprites and inferences are made about the distribution of charge in the parent discharge. Also, evidence is presented which suggests the large and rapid charge transfers of sprite-producing discharges may often adversely affect tall metallic structures on the ground.
In Chapter 4, the comparison of photometry with ELF data of sprites is reviewed. These comparisons revealed that sprites emitted a unique ELF signature. The unique sprite signature was recently used in a collaborative effort to report the first detection of daytime sprites (Stanley et al., 2000). The charge moment changes of the parent discharges and the daytime sprites are presented. The charge moment changes of the parent discharges at the onset of the sprite ELF signatures are compared with conventional breakdown theory.
High-speed video of sprites is analyzed and correlated with the charge moment changes of the parent discharges (and sprites) in Chapter 5. The initial development of sprites based on the high speed video data was published (Stanley et al., 1999) along with a comparison of sprite development with charge moments based on ELF measurements (Cummer and Stanley, 1999). High speed video data obtained of sprite halos was recently compared with the theoretical predictions of Pasko et al. (1997a) by Barrington-Leigh et al. (2000). Most of the data presented in this chapter are of sprites which were not included in the above papers. Some additional conclusions are drawn and the charge moment threshold and apparent altitude of sprite initation are compared with conventional breakdown theoretical predictions.
In Appendix A, the characteristics of the high-speed video system is shown. Also, the data acquisition system which was used to acquire broadband sferic data is described. The calibration of the various instruments is described in Appendix B. Finally, the effect of ionospheric images on static electric field measurements at ground-level is explored in Appendix C and these results were used to calculate the charge moments in Chapter 3.