近地雷暴电场与羊八井地面宇宙线关联的模拟研究

雷暴期间地面宇宙线强度变化的研究对理解大气电场加速宇宙线次级带电粒子的物理机理具有重要意义. 分析西藏羊八井ARGO实验中2012年大气电场的数据后发现, 近地雷暴电场的强度可达1000 V/cm甚至更高. 用Monte Carlo方法模拟研究了近地雷暴电场与羊八井地面宇宙线强度的关联. 当雷暴电场强度(取1500 V/cm)大于逃逸电场时, 宇宙线次级粒子中正、负电子的数目呈指数增长, 在大气深度约520 g/cm²处达到极大值, 与Gurevich等提出的相对论电子逃逸雪崩机理和Dwyer理论相符. 当雷暴电场强度小于逃逸电场时, 在所有负电场范围和大于600 V/cm的正电场范围, 总电子数目随电场强度的增大而增加; 当正电场小于400 V/cm时, 总电子数目均出现一定幅度的下降; 在电场为400–600 V/cm范围内, 总电子数目的变化与原初粒子的能量有关, 原初能量小于80 GeV时, 其次级粒子中总电子数目增加, 原初能量在80–120 GeV 范围内时, 总电子数目变化不明显, 原初能量大于120 GeV时, 总电子数目出现下降, 下降幅度约4%. 模拟结果可对羊八井ARGO实验的观测结果给予合理的解释.

Simulation study on the correlation between the ground cosmic rays and the near earth thunderstorms electric field at Yangbajing (Tibet China)

Coincident study on the intensity change of the ground cosmic rays during thunderstorms is very important for understanding the acceleration mechanism of secondary charged particles caused by atmospheric electric field. It is found that the strength of the near earth thunderstorm electric field can be up to 1000 V/cm or even higher from ARGO-YBJ (where YBJ stands for Yangbajing, 4300 m a.s.l., Tibet, China) data in 2012. In this paper, Monte Carlo simulations are performed by using CORSIKA program to study the correlations between the intensity of the ground cosmic rays and the near earth thunderstorm electric field at YBJ. When the atmospheric electric field strength is higher than the threshold field strength (E_RB) for the development of a runaway breakdown process, the total number of electrons and positrons is exponentially increases. At an electric field strength of 1500 V/cm, the number increases exponentially and reaches a maximum value at an atmospheric depth of ～520 g/cm², where the electric field is slightly stronger than the threshold field strength. These results are consistent with the theoretical results of relativistic runaway electron avalanche (RREA) which was proposed by Gurevich et al. (Gurevich A V, Milikh G M, Roussel-Dupre R 1992 Phys. Lett. A 165 463) and also supports Dwyer's theory. The total number of electrons and positrons increases with the strength of the field in the negative field or in the positive field greater than 600 V/cm, while a certain degree of decline occurs in the positive field less than 400 V/cm. In the range 400-600 V/cm, the energy of the primary proton should be taken into account. For the primary energy that is lower than 80 GeV, the total number of electrons and positrons increases. And it does not change obviously when the energy is between 80 GeV and 120 GeV. For the primary energy exceeds 120 GeV, the number drops off, and the decrease is of ～4%. During thunderstorms, a short duration occurs in which the single particle counting rate increases as energy lowers, while a decrease happens with energy becoming higher than that from ARGO-YBJ data. Our preliminary results can give reasonable explanations to the experimental observations of ARGO-YBJ.