The Faraday rotation and amplitude data for the period September 1978 through August 1979, recorded from the geostationary satellite SMS (90¿W) at Natal (5.9¿S, 35.2¿W), have been utilized to study the behavior of total electron content (TEC). Apart from diurnal and seasonal behavior of TEC, two characteristic features of the nighttime ionosphere are discussed: (1) a postsunset enhancement in TEC which lasts for several hours following the rapid sunset decrease and (2) the sharp, isolated changes in TEC. In particular, relating to phenomena 2, the depletions in TEC are usually accompanied by a simulataneous increase in fading rate, scintillation index, and amplitude The statistics of their occurrence and nature are described. The average behavior of the signal amplitude after propagating through either a depleted or an enhanced ionosphere is modeled theoretically and shown to be in agreement with the observed experiment behavior.