Annual and semiannual periodicities in NmF2 in the African sector

Abstract

The annual and semiannual periodicities in amplitude and phase of NmF2 have been computed for eleven stations in the African sector. The computations are for the sunspot maximum years of 1958 and 1968 and the solar minimum of 1964. Four patterns of diurnal behaviour in NmF2 are discerned for different dip latitudes. The annual amplitude component is small in all sectors at low dip latitudes, however, at higher latitudes it is much larger in the northern hemisphere than the southern hemisphere at sunspot maximum. The annual phase occurs generally in December/January whilst the semiannual phase is in October/April. Comparisons made with the American and Asian sectors show little difference between the three sectors, however, greater similarity exists between the African and Asian sectors than with the American sector. Distinct differences in NmF2 behaviour occur between the northern and southern hemispheres.