Observation of the thunderstorm-related ground cosmic ray flux variations by ARGO-YBJ

TL;DR

This study demonstrates how thunderstorms influence ground cosmic ray flux, revealing electric field effects on secondary particles, with implications for understanding atmospheric particle acceleration during storms.

Contribution

First to explain the variation of cosmic ray flux during thunderstorms through electric field effects on secondary particles, supported by ARGO-YBJ data and Monte Carlo simulations.

Findings

Cosmic ray flux varies with electric field polarity and strength during thunderstorms.

Electric fields in a few hundred meters of atmosphere modify secondary particle energies.

Observed flux variations are explained by electric field acceleration/deceleration of charged particles.

Abstract

A correlation between the secondary cosmic ray flux and the near-earth electric field intensity, measured during thunderstorms, has been found by analyzing the data of the ARGO-YBJ experiment, a full coverage air shower array located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China). The counting rates of showers with different particle multiplicities, have been found to be strongly dependent upon the intensity and polarity of the electric field measured during the course of 15 thunderstorms. In negative electric fields (i.e. accelerating negative charges downwards), the counting rates increase with increasing electric field strength. In positive fields, the rates decrease with field intensity until a certain value of the field EFmin (whose value depends on the event multiplicity), above which the rates begin increasing. By using Monte Carlo simulations, we found that this peculiar behavior can be well described by the presence of an electric field in a layer of thickness of a few hundred meters in the atmosphere above the detector, which accelerates/decelerates the secondary shower particles of opposite charge, modifying the number of particles with energy exceeding the detector threshold. These results, for the first time, give a consistent explanation for the origin of the variation of the electron/positron flux observed for decades by high altitude cosmic ray detectors during thunderstorms.