General Features of the Ionosphere at Thumba

Abstract

The paper describes the characteristics of the ionosphere over the magnetic equator as revealed from the ionograms obtained by an automatic ionospheric sounder at Thumba. The well-known midday biteout of the f0F2 at the equatorial stations is almost absent during the winter months and is most pronounced during the equinoxes. The equinoctial maxima of f0F2 seem to be more pronounced for the midnight than for midday hours. The solar cycle variation of f0F2 for any particular solar hour are inversely proportional to the changes in the F2-layer height during the same period. Another interesting feature of the F2-layer at Thumba has been the development of extremely pronounced and sharp peak of hpF2 around 20 hr during the equinoxes. The absence of ionospheric echoes in the early morning hours is very predominant during the low sunspot years. The spread-F at Thumba is of range splitting type during early part of the night and frequency spread type during early morning hours. The midday f0F2 at Thumba are less ...