Study of the characteristics of rocket-triggered lightning energetic radiation and its relationships with the discharge parameters

Through the use of the independently developed Thunderstorm Energetic Radiation Observation System (TEROS), observation experiments of rocket-triggered lightning energetic radiation (RLER) were conducted for the first time at the Field Experiment Base on Lightning Sciences, China Meteorological Administration from May 2021 to July 2021. A total of 17 X-ray bursts were detected during all of the 22 leader/return strokes. In this study, the energy, time, and direction characteristics of X-ray burst and its relationships with the corresponding discharge parameters, such as the return stroke peak current, half-peak width, rise time, and interstroke time interval, as well as the associated physical processes, are analyzed and discussed. Results showed that energetic radiation is ubiquitous in triggered lightning and is closely related to the last downward leader phase before the return stroke. The photon energies were concentrated in tens to hundreds of keV, and the average duration of RLER was approximately 27 µs. Moreover, RLER exhibited directional property inconsistent with a vertical downward beam, which may be related to the development orientation of the lightning leader. The intensity of RLER was positively correlated with the return stroke peak current, indicating that it directly depends on the lightning intensity, but it would be modulated by the lightning channel conditions. The 17 RLER events showed 3 different time distribution patterns, namely, discrete, continuous, and discrete/continuous pulses, of which the discharge parameters were also different. The discrete pulse event had the longest duration, a small half-peak width, and a long interstroke time interval. Furthermore, all of these events occurred during the last several leader/return strokes. The continuous pulse event had a short duration and a small peak current. The discrete/continuous pulse event had a moderate duration and a large half-peak width and peak current. These three distinct time distribution patterns may be determined by different development types of lightning leaders. Our observations support the leader high-field runaway mechanism.