Numerical simulation of nighttime electron precipitation in the lower ionosphere over a sub-auroral region

Abstract

This work presents computational simulations of electron precipitation events in the lower ionosphere to explain 30 MHz riometer absorption events registered at the Brazilian Antarctic Station – BAS (62.56°S; 58.39°W). The simulations are based on the calculation of ion production rates from different sources (interplanetary and geocoronal ultraviolet radiations, energetic electrons and cosmic rays) and the use of a detailed ion chemical scheme to obtain the electron density which is then used to calculate the absorption at 30 MHz. The electron density calculations were performed using the continuity equations for 25 positive ions and 10 negative ions, involving 175 chemical reactions, that are solved under chemical equilibrium condition. The simulation results show that a flux of ≈2.5 × 10 6 electrons cm −2 s −1 can increase the ionospheric cosmic noise absorption by 1 dB. The results also show that the amplitude of the maximum absorption is sensitive to variations in the precipitated electron flux in the energy range of 98–320 keV that affect most the height region of 65–85 km, and that a larger contribution of the ionospheric absorption due to electron precipitation arising from above the height of absorption peak (rather than from below it), that is, the lower energy range of the precipitated electron spectra has a more dominant contribution to the attenuation of the galactic cosmic noise signal.