Discussion and conclusions
Strong electric fields in thunderclouds give rise to RREAs, which end up as TGEs registered by surface particle detectors. Observation of three sequential TGEs at the end of May 2021 allows us to understand the interrelation of particle fluxes and the structure of the atmospheric electric field.
For the first time, we describe an EOSO accompanied by the graupel fall and intense flux of the gamma rays and electrons. The sequence of the oscillations of the NS electric field along with the dynamic of the registered TGE flux and graupel fall proves the EOSO model as a sequent lowering and decaying of the tripole charged layers. Three TGEs observed at the end of May 2021 on Aragats demonstrate a rich variability of the electron accelerator operation modes depending on the proximity of the particle detector site to the active storm zone.
On 23 May when the storm was just above particle detectors (at distances 1.6 – 5.4 km) nearby lightning flashes terminate RREA after a few tens of seconds. If the storm active zone is far away from particle detectors (>10 km) the TGE extends 12 and 18 minutes and smoothly terminates when conditions of the atmospheric electric field fail to support RREA. Thus, the RREA can be unleashed in a very large spatial domain around the storm, reaching several km in radii. From the energy spectra of a TGE registered on May 30, 2018 (Chilingarian et al., 2018) we estimate the total number of gamma rays (with energies above 300 keV) hitting the earth’s surface to be 1.3*106/m2min. Assuming that ≈ 2000 thunderstorms are active on the globe and that the overall surface of the thunderous atmosphere each moment can be estimated as 2.000 * 100 km2 = 200,000 km2 (0.04% of the globe surface), we come to an estimate of ≈1016 gamma rays are hitting the earth’s surface each second!