Pattern of F2-layer peak electron density across African Ionosonde locations and response to solar activity

Abstract

The diurnal, longitudinal, and latitudinal characteristics of the F2-layer peak electron density (NmF2) at six African stations comprising mid- and equatorial latitudes was investigated. The study covers years of low- (F10.7 = 82.2sfu) and high- (198.6sfu) solar activities. The results revealed that the NmF2 noontime-bite-out was prevalent only in the equatorial latitude. There is latitudinal (geographic) influence on the NmF2 pre-noon and post-noon peak magnitudes at the equatorial locations irrespective of solar activity. The pattern of the NmF2 amplitude during some selected specific time showed that the noontime-12LT, sunset-18LT and midnight-00LT observations are latitudinally inclined, whereas that of the sunrise-06LT is longitudinally-based for both conditions of solar events. Generally, there is a semi-annual asymmetry in the NmF2 monthly pattern with peaks in the equinoctial months. This asymmetry is significant at equatorial latitudes at daytime (06LT/12LT) and nighttime (18LT/00LT) but absent at nighttime of mid-latitudes. The asymmetry feature at the equatorial stations finds its explanation in the ionization anomaly being triggered by the fountain effect mechanism. The NmF2/F10.7 pair correlation (r) presents highest value at 06LT at all equatorial stations for both conditions of solar activity. Generally, r is higher during LSA than during HSA, and finds its explanation in the rate of ionized neutral species and ionospheric electrodynamics. The equatorial noontime bite-out amplitude (bite-outamp) is highest in equinoxes and is latitudinally inclined. We obtained a higher bite-out intensity at the equatorial stations during the HSA than the LSA period by a factor of ≈ 41 %. The importance of thermospheric neutral winds in the large-scale distribution of plasmas was emphasized.