study of simultaneous detection of the ionospheric cosmic noise absorption transient events over sub-auroral and south atlantic geomagnetic anomaly region from 1989 to 1996

For over fifty years, the absorption of cosmic noise has been used as a mean to investigate the lower ionosphere and, indirectly, the influence of the solar activity in the ionosphere. In this work, simultaneous records during the solar maximum activity (between 1989 and 1991) of the sudden increase of the ionospheric cosmic noise absorption registered by riometer data operating at 30 MHz (Relative Ionospheric Opacity Meter) from Cachoeira Paulista (22.58° S; 45.0°W -- in the South Atlantic Geomagnetic Anomaly region) and Brazilian Antarctic Station -EACF ( 62.56S; 58.39W -- in the sub-auroral region) are presented. These events are compared with solar proton and electron flux data at different levels of energy (recorded by satellite - GOES 6 and 7) and geomagnetic index data. A previous analysis of this result suggests that the sudden increases of lower ionosphere ionization in those stations arises from the interaction of the solar cosmic ray particles with the neutral atmosphere. These types of events can be interpreted as a result of the sudden mass ejection from the solar coronal region in a short time space (solar flare) reaching the lower altitudes (populated by heavy neutral molecules with high density) and ionizing this region when it arrives in the terrestrial atmosphere at different latitudes.