# Thermospheric Neutral Wind Measurements and Investigations across the African Region--A Review
## 3 Measurements of Meridional Wind Magnitudes and Directions  
The typical scenario of the meridional winds reported is that the winds are poleward in the early evening hours. The directions switch to the equatorward direction towards midnight. This reversal often happens between 20:00 and 22:00 LT. Then the peak of the equatorward wind is attained around local midnight and the equatorward magnitude decreases thereafter, even returning to the poleward direction for some nights. This pattern is consistently reported in the works of [4; 7; 13; 17; 23; 24; 25; 26; 27]. There are, however, some exceptions to this pattern. For example, in the Nigerian region [4], the early evening winds were sometimes observed to be equatorward with small and decreasing magnitudes, then turning poleward within 1-3 h of sunset. This pattern was observed in the months of March-June and September, whereas the early evening poleward winds were observed in the months of October to January. In the equatorial region of Brazil (geographic: 6.87\({}^{\circ}\) S, 38.56\({}^{\circ}\) W; geomagnetic: 5.73\({}^{\circ}\) S and geographic: 7.38\({}^{\circ}\) S, 36.52\({}^{\circ}\) W; geomagnetic: 6.81\({}^{\circ}\) S), the results of [PERSON] et al. (2015) [17] showed similar results, but during contrasting months. The cases of early evening equatorward winds were observed around the months of October to January, while the early evening poleward winds were conspicuous around the months of April to August. The reason for the contrasting months can be explained to be as a consequence of the equatorial location of both stations but in opposite hemispheres. The Nigerian and Brazilian stations are both located in the equatorial region, but the Nigerian station is in the northern hemisphere, while the Brazilian station is in the southern hemisphere. The reason is that the trans-equatorial winds which are observed as equatorward in Nigeria will be observed as poleward in Brazil, and vice versa. During the geomagnetic storm of 27-28 February 2014, the results of [PERSON] et al. (2018) [25] also indicated an early evening equatorward wind, which mostly remained equatorward until 2 h after local midnight. Clear seasonality can be seen in the reports of Morocco and South Africa because these are mid-latitude stations. Figures 2-4 represent some of the plots of the meridional winds in Morocco, South Africa, and Nigeria, respectively. The equatorward winds are faster in summer than in winter [13; 17; 26]. Morocco (South Africa) is in the Northern (Southern) hemisphere, and so local summer occurs during the months of June-August (November-January), while winter occurs during November-January (June-August). In Morocco, the peak equatorward magnitude is slightly greater than 100 m/s during summer, but the equatorward magnitudes are reduced or non-existent during winter [17; 23]. In South Africa, the peak equatorward magnitudes grow to \(\sim\)100 m/s during both winter and summer. The difference between winter and summer, however, is that the winds are predominantly equatorward (in terms of duration) during local summer [13]. Figure 2: Meridional winds in Morocco for January 2014 to February 2016. The blue plots represent the FPI measurements, while the green plots represent corresponding HWM-14 predictions. The vertical error bars indicate the standard deviations of the observations. Adapted with permission from Ref. [23]. 2017, [PERSON] et al. The meridional winds are faster during periods of higher solar activity [30]. The solar activity term used here refers to the activity of the Sun which changes over \(\sim\)11-year cycle, as quantified by parameters such as the sunspot number, F10.7, etc. For example, [PERSON] et al. (2015) [17] and [PERSON] et al. (2017) [23] both used data from the Morocco FPI. Their observations are both consistent with regards to the note that the equatorward winds peak around midnight during summer, but the peak magnitudes reported by [PERSON] et al. (2017) [23] are smaller (\(\sim\)75 m/s) than those reported by [PERSON] et al.