The Second LHAASO Collaboration Conference in 2026 & The Academic Symposium for the 10th Anniversary of the LHAASO collaboration

Terrestrial gamma-ray flashes (TGFs) are high-energy particle bursts originating from the Earth's atmosphere, typically accompanied by thunderstorm and lightning activity. The relativistic runaway electron avalanche (RREA) mechanism is widely considered responsible for the production of TGFs. In this work, Monte Carlo simulations are conducted with the CORSIKA package to investigate the RREA process initiated by seed electrons of varying energies at different altitudes. The results show that the intensity of secondary particles in the RREA process decreases rapidly with increasing altitude and exhibits only a weak dependence on seed electron energy. At altitudes above 10 km, the energy distributions of RREA particles become increasingly dependent on the seed electron energy, with higher seed energies leading to a larger proportion of high-energy secondary particles. After leaving the RREA region, the survival ratios of secondary particles decrease rapidly with decreasing altitude. At altitudes below 10 km, they show a weak dependence on seed electron energy. The relationship between the source altitude of the RREA process and the secondary particle intensity at the LHAASO site is also simulated. The results show that the farther from the RREA source region, the lower the survival ratio of ground-level particles, decreasing from ~80% at an attenuation distance of 20 m to ~5% at 1000 m.