Study of Regular Variations in Vertical Total Electron Content (VTEC) from 2013 to 2021 at Station BF01 in Ouagadougou

This paper presents the regular variations of the Vertical Total Electron Content (VTEC) at station BF01 (Lat. = 12.3714 N and Long. = -1.5197 W) in Ouagadougou (Burkina Faso) located in the trough of the equatorial ionisation anomaly near the northern ridge of the West African zone. The period studied runs from 2013 to 2021. The VTEC is extracted from the raw Global Navigation Satellite System - Continuously Operating Reference Station (GNSS-CORS) data recorded at station BF01 during the study period. The analysis of diurnal variations showed three types of profiles with a dominant profile being the Dome type. Generally speaking, the daily VTEC profiles show a minimum at dawn between 4:00 UT and 6:00 UT followed by a rapid increase from sunrise to a maximum around 15:00 UT, then a gradual decrease in the late afternoon and during the night to reach the minimum just before sunrise. On some days, a second nocturnal maximum is observed between 19:00 UT and 20:00 UT. Seasonal and annual variations revealed that for each year, the highest VTEC values are observed during the equinox, although with higher values at the March equinox. It was also found that the lowest VTEC values are recorded at the summer solstice in each year. The regular variations in the VTEC at station BF01 during the study period therefore highlight three anomalies: the semi-annual anomaly, the equinoctial asymmetry and the winter anomaly. Furthermore, the VTEC at station BF01 in Ouagadougou evolves in phase with the sunspot cycle.