Effect of near-earth thunderstorm electric field on the flux of cosmic ray air showers in LHAASO-KM2A

TL;DR

This study uses simulations to analyze how near-earth thunderstorm electric fields influence cosmic ray air shower fluxes detected by LHAASO-KM2A, revealing dependencies on electric field strength, polarity, and atmospheric conditions.

Contribution

It provides the first detailed simulation-based analysis of the effects of thunderstorm electric fields on cosmic ray shower rates at LHAASO-KM2A, highlighting key dependencies and variations.

Findings

Shower flux increases with negative electric field strength, up to over 12%.

Flux variation depends on electric field polarity, intensity, and atmospheric layer thickness.

Lower primary energy events are more affected by thunderstorms than higher energy events.

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) is located at Haizi Mountain, Daocheng, Sichuan province, China. Due to its high-altitude location with frequent thunderstorm activities, the LHAASO is suited for studying the effects of near-earth thunderstorm electric fields on cosmic ray air showers. In this paper, Monte Carlo simulations are performed with CORSIKA and G4KM2A to analyze the flux variations of cosmic ray air showers detected by the kilometer-square array of LHAASO (LHAASO-KM2A) during thunderstorms. The strength, polarity, and layer thickness of atmospheric electric field (AEF) during thunderstorm are found to be associated with the shower rate variations. The flux of shower events satisfying trigger conditions of the KM2A increases with field intensity, particularly within negative fields, and the enhanced amplitude is more than 5% in -600 V/cm and 12% in -1000 V/cm, whereas it increases by only 1% and 7% in equivalent positive fields, respectively. While in positive fields ranging from 0 to 400 V/cm, the shower rate decreases with smaller amplitudes. Furthermore, the shower rate increases dramatically with the AEF layer thickness until a certain value, above which the variation trend slows down. The dependence of the trigger rate variation on the primary zenith angle has also been revealed, increasing in lower zenith angle ranges and showing opposite behaviors in higher ones. Additionally, we study that the relationship between the trigger rate variations and the primary energies, and find the enhanced amplitude of the shower rate decreases with increasing primary energy. Simultaneously, the shower events with lower primary energy show a significant increase, whereas events with higher primary energy are hardly affected during thunderstorms. Our simulations offer insights into the variation of the trigger rate detected by LHAASO-KM2A during thunderstorms.