## 3 Results and Discussion  
### Ionospheric Conditions  
It has been established that the total electron content (TEC) is a good parameter to monitor and provide an overall description of the ionosphere over any location [4; 38]. In this work, due to the paucity of data in the region under investigation, it became necessary to use gridded data obtained from the NASA webpage ([[https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html](https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html)]([https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html](https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html)), website accessed on 23 November 2023). The available observational data from ground-based GNSS stations were compared with the gridded data (Figure 3). We obtained slope values of 0.93 and 0.91 for Lagos and Abuja, respectively. This shows that 0.93 and 0.91 units in the observational data correspond to 1 unit in the model data. This shows that the NASA model data adequately represented the observational data. The correlation values of 0.92 obtained at both locations further confirmed this. This is in agreement with other studies that have validated a couple of modeled VTEC data with observational data [39; 40]. Due to its good performance, the present work considered the NASA model's VTEC data. The TEC's time series plots are presented in Figure 4, while the seasonal variation in DFS is shown in Figure 5. Figures 6 and 7 show the ionosphere's condition during the study period.  
Figure 5: Seasonal variation in DFS over a period of two years.  
Figure 6: Contour plots of the hourly values of VTEC for the year 2020 (**upper** and **lower** panels show the variation over Abuja and Lagos).  
The ionospheric TEC displays the signature diurnal and seasonal patterns, as observed in Figures 6 and 7. The figures show that the TEC has higher values during the daytime compared with nighttime values at the two stations and across the months. Generally, and under normal quiet conditions, the ionospheric TEC values generally increase from their minimum at the pre-sunrise time of 0600 h UT in all the seasons and reach their maximum value during 1200 h and 1400 h UT. These diurnal variations have been attributed to extreme ultraviolet flux, geomagnetic activity, equatorial electrojets, and local atmospheric conditions in the thermosphere [41; 42].  
Also, the figures display a conventional semiannual seasonal variation pattern, where TEC values are greater at the equinoxes and lower at the solstices. [PERSON] et al. [31], citing previous works, explained that the seasonal variation of ionospheric TEC over nine Nigerian stations, which included Lagos and Abuja, could be due to any or a combination of the following: seasonal changes in atmospheric composition [43; 44; 45], changes in atmospheric turbulence, inputs from atmospheric waves, and variations in geomagnetic activities [46], among others. It is pertinent to acknowledge that the condition of the ionosphere and its variability over the stations of interest have been discussed by [PERSON] et al. [31], and the references therein.