AbstractThe phenomena of ‘spread echoes’ on vertical incidence ionospheric soundings and ‘flutter fading’ on short-wave C.W. transmissions are of frequent occurrence in the low equatorial latitudes. Both the phenomena are predominant after local sunset and are inhibited during periods of strong magnetic activity associated with magnetic storms. A physical explanation is offered in this paper to the origin of these two phenomena in the following manner: Marked increase in the height of the F region of the ionosphere is almost a daily occurrence immediately after local sunset in low equatorial latitudes where the F region often ascends beyond 500 to 600 km. in the evening hours. The Allen radiation belt, recently discovered from satellite explorations, reaches down to a level of 500 miles or so from the surface of the earth over the equatorial regions. The F layer, during its. upward ascent, is likely to touch the lower fringe of this radiation belt and since this belt consists of high energy charged partic...