Long lasting low energy thunderstorm ground enhancements and possible Rn-222 daughter isotopes contamination

Abstract

Thunderstorm ground enhancements (TGEs) comprise large particle fluxes coming from the clouds that usually coincide with thunderstorms. Most of TGEs observed at the Aragats research station in Armenia during the last ten years originated from ``beams of the electron accelerator'' operating in the thunderclouds above the research station. Observed TGEs contain high-energy electrons and gamma rays (as well as neutrons) and usually last a few minutes. Starting from 2014, we use particle detectors tuned for the registration of lower energies particles coming from thunderclouds (starting from 0.3 MeV). In 2016, we already noticed that TGEs measured by particle detectors with a low energy threshold demonstrated a drastically larger duration. The flux of the high-energy particles (with energies up to 40 MeV) lasts 1--10 min; the lowest ones (less than 3 MeV)---more than two hours. All intense TGEs contain a high-energy peak and a prolonged low-energy extension lasting 2--3 h. In the presented paper, we describe examples of long-lasting TGEs and discuss correlations of enhanced particle fluxes with disturbances of the electric field and with precipitation.