Enhancements and sharp depletions of total electron content in the nighttime equatorial ionosphere

The considered study is based on two years of continuous measurements of the total electron content (TEC), taking into account the time from September 22, 1978, through December 21, 1980. The observation period is near the maximum of the present solar cycle. Topside density measurements in the evening sector over the Atlantic Ocean near the maximum of the last solar cycle at altitudes greater than 600 km, suggest that TEC measurements should be highly structured at Ascension Island. Basically two effects are being considered, including the large postsunset enhancements, and the sharp structures, usually depletions, associated with them