Relationship Between X-Rays and the Propagation Speed of Downward Negative Leaders in Rocket-Triggered Lightning

On 18 July 2023, X-ray emissions associated with two rocket-triggered lightning flashes were observed at the Field Experiment Base for Lightning Sciences, China Meteorological Administration. In this paper, the relationship between X-ray characteristics and propagation speed of downward negative dart leaders is analyzed for the first time. Results show that within the same lightning flash, there is a strong positive correlation between the leader brightness and its 2D speed, as evidenced by a high correlation coefficient, R, of +0.94. Consistently, the intensity of X-rays generally exhibits a positive correlation with the leader 2D speed. Conversely, the average X-ray pulse interval is negatively correlated with the leader 2D speed, with a significant correlation coefficient, R, of −0.93. Furthermore, the intervals of partial steps of dart leader can be characterized by the intervals between the X-ray pulses.