Electrical Structure and Preliminary Breakdown of Lightning Flashes in Three New Mexico Thunderstorms

In this presentation, we compare propagation characteristics of lightning flashes from Lightning Mapping Array data to simultaneous electric field (E) measurements at different altitudes for three storms. For normal cloud-to- ground flashes, detailed analysis has shown that when a potential well for negative charge exists between the altitude of the flash initiation and ground, the first return stroke occurs only after a period of horizontal negative polarity branching below the initiation altitude. This period of preliminary breakdown, or the delay between the initiation time and the first return stroke, lasted an average of 117 ms for 14 flashes that initiated when a low-level potential well was present. When no low-level potential well was indicated in the E data, the time between flash initiation and first return stroke averaged 15 ms. Existence of preliminary breakdown for more than about 40 ms before the first return stroke of a cloud-to-ground flash thus suggests that a low-level potential well for negative charge is present at that time in the storm. Examples will be shown that give an indication of the rapid temporal evolution in the electrical structure of the storm as it relates to the lightning activity.