Nevertheless, the issue of streamer initiation is addressed in the context of the observations presented in subsequent sections. The requirements for streamer initiation have mostly been discussed in the context of spark-gap experiments. For instance, Raizer et al. Such considerations are appropriate for an avalanche starting from a narrow point and expanding in a gas of uniform density. Raizer et al.
Electric field thresholds for air breakdown mechanisms.
Breakdown electric field as a function of altitude is shown for conventional and relativistic runaway breakdown. In addition, minimum fields required for propagation of several discharge processes are shown. Figure 2.1 shows electric field thresholds required for air breakdown as a function of altitude. Conventional breakdown occurs at 32 at ground level and follows the neutral density to 2 at 70 km and 8 at 90 km altitude. Once a streamer is initiated, it may propagate in electric fields lower than .