Transient UV Background when Registering EASes with the TUS Orbital Detector

The TUS detector is the first orbital telescope designed to test techniques for measuring ultraviolet fluorescence and Cherenkov radiation of extensive air showers (EASes). The detector was launched aboard the Lomonosov satellite on April 28, 2016. A two-level event selection system (trigger) was developed and implemented in the digital electronics of the photodetector. This trigger was optimized for the search for EASes, but at the same time operated under conditions of variable atmospheric luminescence of both natural (aurora light, diffused moonlight, thunderstorm phenomena) and anthropogenic origin (city lights, flashes at airports). The frequency of the trigger also depends on that of transient atmospheric phenomena of different origin. Examples of events recorded by the TUS detector and selected welve by the EAS trigger are given.