Abstract
The comparative analysis of three thunderstorms on Aragats in May 2021
demonstrates that relativistic runaway electron avalanches (RREAs) are
developing in large areas of the thunderous atmosphere. In the active
storm zone, RREAs last tens of seconds to a few minutes, until lightning
flashes terminate electron acceleration. Thus, RREAs development is
paired with lightning activity, creating huge electron fluxes preceding
the development of lightning leaders. If the lightning activity is far
from the detector site, measured particle fluxes (thunderstorm ground
enhancements - TGEs) are smoothly enhanced and decayed when the
atmospheric conditions cannot anymore sustain the electron runaway
process. In this case, the TGE has a more or less symmetrical shape and
can last up to 10 minutes and more. Thus, the total surface area exposed
to ionizing radiation can reach 100 km2 and total
number of gamma rays directed to the earth’s surface –
2*1018. The differential energy spectra of electrons
and gamma rays recovered by particle spectrometers are used to estimate
the heigh of a strong accelerating electric field region, which can
extend down to tens meters above the earth’s surface.