Effects of geomagnetic mirror force and pitch angles of precipitating electrons on ionization of the polar upper atmosphere

Abstract. We studied the effects of the geomagnetic mirror force on electron density enhancements in the polar atmosphere due to energetic electron precipitation. Using the pitch angle and energy distribution of electrons observed by the low-altitude Electron Losses and Fields INvestigation (ELFIN) satellites as initial conditions, the electron density in the atmosphere caused by precipitating electrons was calculated using a simulation with two different methods: a traditional method that does not include the effect of the mirror force and a recently developed method that includes the effect. From a simultaneous observation event of the ELFIN satellite and the European Incoherent SCATter scientific radar system (EISCAT) Tromsø radar, it was found that the method with the effect of the mirror force reduces electron density by about 40 % at an altitude of 80 km compared to the traditional method. This decrease was pronounced when the pitch angle distribution of high-energy electrons was concentrated in the pitch angle range of the trapped component and near the loss cone. The maximum decrease was 50 %. For an event where the altitude profile of electron density was accurately determined from the EISCAT radar, the electron density profile estimated using the method with the effect of mirror force showed better agreement with the electron density profile derived from the EISCAT radar. The comparison between simulation results and the observation data contributes to the establishment and improvement of atmospheric ionization models using various types of precipitating electrons.