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A gamma ray glow (GRG) is a long-lasting x-ray and gamma radiation generated in thunderclouds. It may last from seconds to several minutes and contain photons with energies exceeding 5 MeV. The brightest GRG may be one or two orders of magnitude higher than the background due to cosmic rays. Energetic x-rays produced by GRG and emitted upwards from the thundercloud may strongly affect the chemical-physical conditions of the stratosphere through additional ionization. The ionization has several effects that we plan to quantify in this project by theoretical modeling: 1. It interacts with the atmosphere to produce nitric oxide, a powerful agent which reduces the ozone layer. 2. The ions serve as seeds for condensation, which leads to an increase in stratospheric aerosol content. 3. The increased ionization leads to increased conductivity in stratosphere. This affects currents flowing in the global electrical circuit (GEC). The ionization effect of GRG is different from cosmic-ray-induced ionization, not only because the flux of x-rays in GRG may exceed that in cosmic rays by orders of magnitude. Unlike cosmic rays, GRG are localized both in time (last seconds to several minutes) and in space (only exist in the vicinity of a thunderstorm), which may lead to new effects. Preliminary estimates also show that the production of nitric oxide (item 1 above) may be of the same order as the strongest source of this chemical in the stratosphere, namely oxidation of nitrous oxide which diffuses upward from the Earth's surface.