On the nature of optical flashes observed aboard Universitetsky-Tatyana and Vernov satellites

Abstract

A model of electric discharges at mesospheric altitudes has been developed to explain the nature of optical flashes/transient atmospheric events (TAEs) observed aboard the Russian microsatellites “Universitetsky-Tatyana-1”, “Universitetsky-Tatyana-2” and “Vernov”. The model is based on assumption that large-scale areas with a low space charge density and a low electric breakdown threshold can occur in the mesosphere thereby producing electric discharges between the charged areas. Variations in the number densities of electrons and ions in the discharge channel connecting these areas are described by kinetic equations, in which spatial derivatives are disregarded. The discharge parameters, such as mobility of charged particles, rate of ionization and rate of electron attachment to neutral molecules are assumed to depend on altitude in the atmosphere. Numerical simulation and analytical solutions of the basic equation set make it possible to analyze the time dependences of electric field, conductivity, current and number densities of electrons and ions in the discharge channel at various altitudes in the atmosphere. Theoretical estimates of the TAEs parameters are best suited to the onboard observations under assumptions that, first, the charged areas of 10−15km in size are situated at altitudes of 60−70km and, second, their total charge is about 1 C. The theory predicts that the energy dissipated during a single electric discharge under these parameters can reach a value from tenths to several MJ while the discharge duration can be on the order of several milliseconds.