Equatorial ionospheric absorption
A study has been made of the variation of absorption with frequency and sun's zenith distance χ at Ibadan at vertical incidence. Since the propagation at Ibadan is almost purely transverse, simple theories in terms of doviative and nondeviative absorption may be applied. It is found that the non-deviative absorption appears to obey a law of proportionality to the inverse frequency. The total absorption varies as (cos χ)n, where n is about 0.7. These variations are accounted tor by assuming that the nondeviative absorption takes place in a Chapman-type D layer at a level where the electron eollisional frequency is of the same order as the angular frequency of the exploring radio signal. Some comparisons are made with the absorption results from other stations. In particular, it is found that the frequency and seasonal variations at Singapore are similar to those at Ibadan.