The existence of an ionized layer in the upper atmosphere was probably already appreciated at the beginning of the last century when Marconi demonstrated that radiowaves could propagate across large distances beyond the free horizon, as if they were guided between a conducting layer and the ground. A conducting layer in the upper atmosphere was also inferred as early as 1880 when studies of diurnal oscillations in the Earth’s magnetic field indicated that these variations might be caused by tidal oscillations in the upper atmosphere.
KeywordsNitric Oxide Total Electron Content Zenith Angle Scale Height Neutral Atmosphere
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