From an analysis of ionogram data of Kodaikanal (dip 3.5 deg N) for a 3-yr period of high sunspot activity, it is shown that the duration of equatorial spread-F (ESF), on the average, bears a direct relationship to the ...

Evidence is presented to point out that the presence of an elevated F-region with reduced peak electron density in the equatorial region does not always result in the occurrence of spread-F condition in the post-midnight period.