Interhemispheric Asymmetry of the Equatorial Ionization Anomaly (EIA) on the African Sector Over 3 Years (2014–2016): Effects of Thermospheric Meridional Winds

Abstract

Abstract Observations made by the Langmuir probes on board the Swarm satellites and the Fabry–Perot interferometer installed at the Oukaimeden Observatory in Morocco have been systematically analyzed to study the effect of geomagnetic activity on the thermosphere–ionosphere system over 3 years. The annual variation of the electron density ( N e ) shows that during the day, the ionospheric density starts to increase at midlatitudes, with a single crest between 8 LT and 12 LT. It is also noticeable that the double crest structure is present between 12 LT and 00 LT: symmetric from 12 LT to 20 LT and asymmetric from 20 LT to 24 LT. Observations show strong seasonal variations, with N e being lower around the June solstice. We have noticed the semiannual anomaly: N e is higher around equinox than around solstice. For solstice seasons, the asymmetries in N e are stronger at the December solstice than at the June solstice. For equinox seasons, we can notice equinoctial symmetry in all local time sectors, meaning that the same trend is observed for both equinoxes with or without symmetrical crests. The effect of meridional neutral winds on equatorial ionization anomaly (EIA) crests have been classified during both quiet and disturbed conditions. Over the studied region, the southward meridional winds have the tendency to enhance the northern crest of the EIA during quiet time and in a more pronounced way during geomagnetically disturbed conditions. Finally, we have quantified the relations between the thermospheric neutral winds data and the EIA by introducing an asymmetrical index.