Ionospheric Responses to CME- and CIR-Driven Geomagnetic Storms Along 30°E–40°E Over the African Sector From 2001 to 2015

In this paper, we present the responses of the ionospheric total electron content (TEC) to coronal mass ejection (CME)- and corotating interaction region (CIR)-driven storms using stations that lie within 30°E–40°E geographic longitude in middle, low, and equatorial latitudes over the African sector. CIR-driven storms are generally weak (−50 nT < Dst < −25 nT) to moderate (−100 nT < Dst < −50 nT) in intensity, while CME-driven storms are often associated with the intense (Dst < −100 nT) geomagnetic storms. CIR-driven storms have long recovery phase as compared to CME-driven storms. CME- and CIR-driven storms were classified based on the features of proton temperature, magnetic field, solar wind speed, and proton density. The storm periods analyzed occurred during the period 2001–2015, which covers part of solar cycles 23 and 24. Disturbance storm time (Dst) ≤ −30 nT and Kp ≥ 3 indices were used simultaneously to identify the storm periods considered. The total number of CME- and CIR-driven storms identified was 148 and 167, respectively. However, due to lack of TEC data, the number of CME- and CIR-driven storms considered for the middle-latitude, low-latitude, and equatorial latitude stations are different for different regions. TEC data used in this study was derived from the Global Navigation Satellite System observations. The statistical analysis of ionospheric storm effects were compared over middle, low, and equatorial latitudes in the African sector for the first time. Negative ionospheric storm effects occurred only during CME-driven storms over midlatitude stations and were more prevalent in summer. For the low and equatorial latitudes, negative ionospheric storm effects were observed during both CME- and CIR-driven storms. Our analysis has shown that positive ionospheric storm effects were more prevalent over middle, low, and equatorial latitudes during both CME- and CIR-driven storms. A significant number of cases where the electron density changes remained within the background variability during storm conditions were observed over the low-latitude stations compared to other latitude regions.