We investigated the American low-latitude ionosphere around 75°W during the two 2013 sudden stratospheric warming (SSW) events: one in quiet geomagnetic conditions, and the other overlapped by a minor geomagnetic storm using total electron content (TEC) data from 12 Global Positioning System (GPS) receivers. A pair of magnetometers revealing the varying inferred vertical E X B drift and the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite airglow instrument to understand the global changes in the neutral composition, O⁄N_2 ratio are also used. The late morning inferred downward-directed E X B drift during the first major SSW did not support the varying equatorial ionization anomaly (EIA) signature. However, during the second major SSW, the well-reported and enhanced late morning inferred upward-directed E X B drift relocated a northern EIA crest to higher latitudes. Interestingly, the effect of a minor geomagnetic storm on 17 January 2013 that modulated the ongoing second SSW reduced the maximum inferred upward-directed E X B drift. The second major SSW contribution to the northern crest is higher than photo-ionization and the first major SSW contribution, while each major contribution is higher than minor warming. The minor geomagnetic storm reduced the effect of the second major SSW on the TEC from 58% to 50% and 28% to 20% at the northern and southern crest, respectively. Also, the storm’s overall effect of - 1 % (22 %) leads to a slight reduction (enhancement) in TEC magnitude at the northern (southern) crest.

The ionosphere around the Equatorial ionization Anomaly (EIA) region exhibits a complex dynamic and responds markedly to the solar-magnetospheric energy and momentum. In this paper, the hourly response of the EIA structure in the Africa to St. Patrick’s Day storms of March 2013 and 2015 is investigated using data obtained from a chain of GPS receivers located in the African region. The TEC variations were characterized based on the convective magnetospheric dynamo fields, the neutral wind circulation, and zonal electric fields. Generally, the result indicates that the TEC variations were consistent with the different directions of the interplanetary fields during the different phases of the storms. We observed reverse EIA structures in the main phase of the storm of March 2015, suggests to be related to the intense PPEF and strong equatorward wind which imposed westward zonal electric field at the equator. Similar equatorial peak observed during the recovery phase is associated to DDEF, poleward wind and plasma convergence. Furthermore, TEC variations also indicate hemispheric asymmetries during the storms. During the main phase, the TEC is more enhanced in the northern hemisphere during the storm of March 2013, this was reversed during March 2015. We observed equatorial peak during SSC period of the storm of March 2013, while EIA structures are generally weak in March 2015 event. This may posit that ionospheric pre-storm behaviour is better understood when the IMF-Bz and electric field are weak. The observed distinctive response avowed the peculiarity in the electrodynamics intricacy in the Africa sector.

In this study, we examine the nonlinear interdependence between the parameters of the solar wind influencing geomagnetic activity (proton density and solar wind dynamic pressure, IMF Bz and solar wind dynamic pressure) and geomagnetic activity (AE and SYM-H) during pre-storm, storm and post-storm of intense, major, moderate and minor geomagnetic storms. Nonlinear analytical tools comprising cross recurrence plot (CRP) and Recurrence Rate (RR) was used to capture the features of nonlinear interdependence in the time series data of the solar wind parameter (solar wind dynamic pressure, IMF Bz and proton density) and geomagnetic indices (AE and SYM-H). The pearson correlation coefficient was also used to reveal the features of linear dependence between the parameters of the solar wind during the different categories of geomagnetic storms. Our result shows that during the storm, the CRPs of the solar wind parameters investigated pictured a strong deterministic structure of CRP which is an indication of strong interdependence. In particular, the results of our analysis showed that the solar wind dynamic pressure and proton density depicted very strong interdependence features. On the other hand, during pre-storm and post-storm, the CRP of solar wind dynamic pressure in relation to IMF Bz and proton density pictured a rare deterministic structure signifying weak interdependence. Furthermore, the values of RR were very high (an indication of strong interdependence between the parameters of the solar wind) during the storm while at pre-storm and post-storm, the values of RR declined significantly in most of the periods which further strengthened the evidence of weak interdependence in the parameters of solar wind. The CRP and RR of the geomagnetic indices (AE and SYM-H) reveals no significant difference between pre-storm, storm and post-storm of the different categories of geomagnetic storms. However, strong interdependence between the geomagnetic indices were observed in most of the periods investigated. Finally, the pearson correlation coefficient reveals high values of linear dependence between the solar wind parameters without any significant difference between pre-storm, storm and post-storm periods during intense, major, moderate and minor geomagnetic storms.

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.