LAUSR

Abstract The model of negative leader in long sparks is the first step to model the upward connecting negative leader (UCNL) from grounded objects for positive cloud-to-ground lightning. In contrast with the upward connecting positive leader, the UCNL is always stepped, which is reproduced in our model. Several assumptions are made in order to simplify the model. We assumed that the difference between the geometrical potential due to the grounding structure and that after corona formation can be used for calculating the charge in the streamer zone. The potential distribution inside the steamer zone was simplified by neglecting the negative streamers near the HV electrode (negative polarity), and the velocity of primary negative leader was set to a fixed value. Different minimum charges required to sustain the extension of the negative and positive parts of space leader prior to its connection to the primary leader were used. The model was verified using experimental datum for negative sparks in 10-m, 16.7-m and 7-m rod-plane air gap. Sensitivity of model predictions to variation in model input parameters was analyzed. The model in this paper can be used to analyze the negative leader propagation in long sparks, which will be extended to UCNL process in the future work.