A case study of the temporal context of narrow bipolar events with ordinary lightning

From analysis of VLF/LF bandwidth electric and magnetic fields and associated VHF emission of 245 NBE-related records during a thunderstorm, the temporal context of NBEs with ordinary lightning discharges was studied. Both negative and positive NBEs could occur in the thunderstorm and -NBEs tended to occur at a much higher altitude than +NBEs. 26 of 377 NBEs were identified as isolated ones since the narrow bipolar pulse was not followed or preceded by any detectable signals within 100ms, while 169 were identified as CG-associated NBEs since the narrow bipolar pulse was followed or preceded by detectable return stroke pulse within 100ms, and the other 182 were identified as IC-associated NBEs. The IC-associated or CG-associated NBEs tend to occur randomly with respect to normal lightning rather than occurring ahead of them. We conclude that NBEs will be produced under conditions which favor the production of normal lightning discharges, but they are unnecessarily related to the initiation of normal lightning discharges.