Influence of variations in the solar hydrogen Lyα radiation on the ionospheric D-region electron density during a year and solar cycle

. The hydrogen Ly α radiation emitted from the Sun is the main source of photo-ionization processes and, consequently, of the free electron production in the ionospheric D-region. Variations in the intensity of the incoming Ly α radiation aﬀect changes in the electron density and they show up as periodic daily and seasonal changes, and changes during a solar cycle. The Quiet Ionospheric D-Region (QIonDR) model describes these periodic changes. In this study, we analyse how changes during a year and changes in the smoothed daily sunspot number (both processes aﬀect the intensity of incoming radiation in the D-region) aﬀect the electron density changes related to quiet conditions. The presented modelling is based on the results of the QIonDR model obtained for the part of Europe deﬁned by the positions of the very low frequency (VLF) signal transmitters ICV (Sardinia, Italy) and DHO (Lower Saxony, Germany), and the AWESOME (Atmospheric Weather Electromagnetic System for Ob-servation Modeling and Education) receiver position (Belgrade, Serbia) in application of the QIonDR model on real signals.