Monte Carlo Simulations of Secondary Cosmic-Ray Variations in Atmospheric Electric Fields : Implications for Long Duration Electron and Gamma-ray Emissions from Thunderclouds

TL;DR

This study uses Monte Carlo simulations to explore how secondary cosmic rays contribute to long-duration gamma-ray and electron bursts from thunderclouds, providing insights into electric field conditions necessary for particle acceleration.

Contribution

It introduces detailed Monte Carlo modeling with realistic cosmic-ray spectra to analyze electric field structures responsible for high-energy atmospheric emissions.

Findings

Gamma rays are the main seed electrons for long-duration bursts.

Electric field strength and structure are constrained by comparing simulations with high-altitude observations.

Simulations help identify conditions for gamma-ray energies exceeding tens of MeV.

Abstract

Monte Carlo simulations were conducted using the Particle and Heavy Ion Transport code System (PHITS) to investigate the role of secondary cosmic rays in the generation of long-duration bursts from thunderclouds and to clarify the conditions of the electric field region responsible for particle acceleration. The simulations utilized realistic secondary cosmic-ray spectra, including gamma rays, electrons, positrons, and muons, as input. The simulation results indicate that gamma rays provide the dominant supply of seed electrons for long-duration bursts, regardless of the geometry or strength of the electric field region. They also reveal the structure and strength of the electric field region required to produce gamma rays exceeding several tens of MeV, which have so far been detected only by high-altitude observations. Furthermore, the fluxes of long-duration bursts estimated from the simulation results were compared with observational data to constrain the properties of the electric field region. In particular, the comparison with measurements at Yangbajing, located at an altitude of 4.3~km, helps narrow down the possible range of electric field strengths and configurations.