Diurnal lower ionosphere electron density variations observed in the South Atlantic Geomagnetic Anomaly and sub-Antarctic region during the occurrence of the major PCA event of 4 August 1972

Abstract

VLF phase and amplitude signals simultaneously received in Atibaia and Curitiba, both in Brazil, were analysed during the occurrence of the major proton flare event of 4 August 1972. Phase advances recorded in Stockholm (Sweden) and Inubo (Japan) were also included for comparison purposes. Particular attention was devoted to the NWC (Australia)-Atibaia (Brazil) propagation-path which passes through disturbed regions (geomagnetically), namely the sub-Antarctic region and the South Atlantic Geomagnetic Anomaly (SAGA), and which propagates completely in the southern hemisphere. Following the current mechanisms that allow charged particles to precipitate at low altitudes in the ionosphere ( Dregion), four regions were defined based on the most significant ‘ L’ value involved. By means of successive comparisons with low and mid latitude propagation paths, some parameters typical of the lower ionosphere were deduced for the southern hemisphere in association with PCA events detected in the polar caps. Fitting exponential models to the data analysed, daytime electron density profiles were obtained for different ‘ L’ values throughout the disturbed period.