An Upward Multi-Pulse TGF Involved With Two Thunderstorm Cells

Abstract

Gamma rays associated with lightning discharges are evidence of $\sim 30$ MeV electrons acceleration by electric field in the atmosphere. However, the acceleration site and actual condition of it are not yet identified. On 30 December 2021, a terrestrial gamma ray flash (TGF) with five (or six) consecutive pulses were detected by our gamma ray detectors placed in Kanazawa City, Japan. Although analog signals of the detectors were severely saturated, timing of the five gamma ray pulses were well constrained and compared with radio observations of discharges. We detected four slow positive radio pulses associated with the first four gamma ray pulses. Another radio pulse candidate associated with the fifth gamma ray pulse was also seen. The polarity of the slow pulses suggests that the TGF were upward directed, and our detectors were observing it backward. This is the first detection of this kind on ground. The radio slow pulses were located in a thunderstorm cell located 3–6 km south from a nearly simultaneously on-going ascending negative stepped leader emerged in another thunderstorm cell. These results suggest that the TGF's acceleration location can be a few km apart from the leader development of the main discharge activity. We also found another ascending negative stepped leader emerging $\sim 32$ ms after the TGF near the region where the five slow radio pulses took place.