Amplitude variations in GPS signals as a possible indicator of ionospheric structures

The noisy and impulsive fluctuations in the CHAMP radio occultation (RO) amplitude data are similar to the C-type and S-type ionospheric amplitude scintillations formerly observed at 1.5 GHz in the mid-latitude region in satellite-to-Earth Inmarsat links. These amplitude scintillations can be associated with different types of ionospheric structures. S-type amplitude variations can be explained by the influence of inclined plasma layers in the ionosphere where the RO signal trajectory is perpendicular to the sharp plasma gradient. Simulation indicates the possibility to reveal the spatial distribution of the electron density in the inclined ionospheric layers from analysis of the S-type RO amplitude variations. The seasonal, geographical and temporal distributions of CHAMP RO events with high S₄ index values observed during the years 2001-2003 indicate their dependence on solar activity.