Calculation of X-ray Emission of Gigantic Upward Atmospheric Discharges Governed by Relativistic Runaway Electrons

On the basis of observation data on space - time characteristics of gigantic upward atmospheric discharges (UAD) there were carried out calculations of X-ray emission produced by UAD, with employing the idea of relativistic runaway electron avalanche. The results are consistent with measurements of X-ray pulses of terrestrial origin detected from satellite above mesoscale thundercloud formations.