Horizontal lightning propagation, preliminary breakdown, and electric potential in New Mexico thunderstorms

Characteristics of lightning flashes in three storms are compared to simultaneous electric field (E) measurements at various altitudes to examine three hypotheses. The first is the idea that horizontal lightning branches propagate at altitudes near potential extrema (or wells). The analyses show that horizontal lightning activity and potential extrema are coincident in time and altitude, and so are consistent with the idea that lightning moves charges into potential wells as a means of using a storm's electrostatic energy to drive a lightning flash's dielectric breakdown processes. Second, these data are used to verify the usual interpretation of breakdown polarity of lightning radiation sources detected by the Lightning Mapping Array. The third hypothesis investigated is that normal cloud‐to‐ground flashes have a period of preliminary breakdown if and only if a potential well for negative charge exists between the altitudes of flash initiation and ground. The analyses show that in 14 flashes when a low‐level well was indicated, the period of preliminary breakdown before the first return stroke lasted an average of 117 ms, considerably longer than the average lifetime of a stepped leader. In 15 flashes in which no low‐level well was indicated, the time between initiation and first return stroke averaged 15 ms.