Investigation of the variability of night-time equatorial thermospheric
winds over Nigeria, West Africa
Abstract
This paper examined the variability of equatorial thermospheric
meridional and zonal wind speeds at night-time using an optical
Fabry–Perot interferometer (FPI) located in Abuja, Nigeria (Geographic:
8.99°N, 7.39°E; Geomagnetic latitude: -1.60). The study period covered 9
months with useable data of 139 nights between March 2016 and January
2018. The hourly zonal wind speed is between 19.33 and 250
ms-1 and that of the meridional wind ranged between 0
and 200 ms-1. These speeds are greater than those
reported in other longitudinal sectors, and this could be one of the
reasons responsible for reduced EXB drift in this region compared to
other regions. Comparison of FPI ground-based measurements with
estimates from the Horizontal Wind Model (HWM-14) accurately reproduced
the meridional component, but for some departure of ~45
ms-1 in May and June 2016, and January 2018. A very
good agreement is observed between the predicted and measured zonal
winds speed in the months of 2017. However, the HWM-14 overestimated the
zonal wind speed in the early evening values by ~30
ms-1 and underestimated the post-midnight values by a
larger factor in December 2017. Hence, this necessitates a call for
improvement of the HWM-14 by using newly observed data in order to
better characterize the West African sector. The varying zonal winds
showed modal periods of 25.9 and 133.5 days, which are quasi 27-days and
quasi-terannual periodic variations, respectively. On the meridional
wind, oscillatory periods of 133.5 and 23.1 days are seen in year 2016
and 2017, respectively.