Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10, 2021*

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) has three sub-arrays, KM2A, WCDA and WFCTA. The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during the thunderstorm on 10 June 2021. The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields, with maximum fractional increase of 20%. The variations of trigger rates (increases or decreases) are found to be strongly dependent on the primary zenith angle. The flux of secondary particles increases significantly, following a similar trend with that of the shower events. To better understand the observed behavior, Monte Carlo simulations are performed with CORSIKA and G4KM2A (a code based on GEANT4). We find that the experimental data (in saturated negative fields) are in good agreement with simulations, assuming the presence of a uniform electric field of -700 V/cm with a thickness of 1500 m in the atmosphere above the observation level. Due to the acceleration/deceleration by the atmospheric electric field, the number of secondary particles with energy above the detector threshold is modified, resulting in the changes in shower detection rate.

Effects of environmental factors on the LHAASO-ED array

“…In other thunderstorm events, increases of the trigger rate are also observed. Recently, thunderstorm ground enhancements (TGEs) and terrestrial gamma-ray flashes (TGFs) are reported in ground based cosmic-ray experiments [7], while further examination is needed to find exact evidence of these phenomena from the experimental data of KM2A.…”

Sinergy of extra-terrestrial particle accelerators and accelerators operated in the terrestrial atmosphere

“…The strength of the atmospheric electric field depends on the air density (altitude) and can reach 1.5-2 kV/cm at altitudes 3-6 km. Several EAS arrays, including those located in Tibet, already report the 20-30% enhancement of the trigger rate during thunderstorms [13][14][15]. Correspondingly, the EAS particle number with energies above the detector threshold is significantly enhanced.…”

“…Correspondingly, the EAS particle number with energies above the detector threshold is significantly enhanced. As a remedy for the shower size artificial enhancement, the shower size was reduced, resulting in changes in the detector trigger rate [15]. At Aragats was registered 400% enhancement of MAKET array trigger rate on 19 September 2019 [2,16].…”