ИСТИНА

Variations of gamma-rays (20 keV – 5 MeV) coming from the atmosphere to the surface level are studied in PGI since 2009 on the station: Barentsburg (arch. Spitsbergen, 78 N), Apatity (Polar cycle, foothills of the Khibiny mountains, 67 N), Rostov-on-Don (plain, 47 N). Detectors are shielded by lead from environment and opened to top. There are two variation kinds: annual and sporadic. The annual variation is more than 30 % with a "winter-spring" depression and a summer flat top on the polar stations. The annual variation exactly follows to thickness of snow cover. At Rostov station the annual variation is absent because the steady snow cover is not in this place. The sporadic variation is called increase event and occurs whole year under solid or liquid precipitation and reach up to 60 % over a clear weather level before. There is a correlation between station latitude and event amplitude too. At the same time there is no increase or variation in the charged particle (muons and electrons) detector. Our hypothesis is on causing by electric field in rain (nimbostratus) clouds. Light charged particles of the secondary cosmic rays gain additional energy in electric field and dissipate it via Bremsstrahlung. The annual variation is not explained now because the station row is short. Now it is found that snow cover lower the gamma-ray flux from the atmosphere. It would be added stations placed in regions with moderate snow cover.