Characterization of the African Ionosphere Variations During Selected Geomagnetic Storms

Yibekal, Kassa Hailu

dc.contributor.author	Yibekal, Kassa Hailu
dc.date.accessioned	2024-11-20T11:18:41Z
dc.date.available	2024-11-20T11:18:41Z
dc.date.issued	2024-10
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/16230
dc.description.abstract	Numerous investigations have looked at the behavior of the African ionosphere dur ing geomagnetic storm events. However, the spatial and temporal variation of the drivers of the ionospheric effect and the characteristics of nighttime ionospheric irreg ularity over the African sector have not yet been investigated in detail using multiple data sources. As a result, this dissertation examines the ionospheric and magnetic signatures of the extreme space weather events that occurred on March 17 and June 23, 2015, over the African sector, as well as the nighttime ionospheric irregularity during August 27, October 7, and December 22, 2015, intense geomagnetic storm events over the Europe-African longitudinal sector at various latitudes. The investigation is carried out using multiple experimental data sets from different sources, including Global navigation satellite system (GNSS) derived TEC data, the geomagnetic field measurements from the International Real-Time Magnetic Obser vatory Network (INTERMAGNET), African B-Field Education and Research (AM BER), and Bureau Central de Magnetisme Terrestre (BCMT) and Swarm satellite in-situ electron density data. To visualise the ionospheric storm effect, the percent age deviation in vTEC was computed with respect to the quiet-time background. We have also studied the magnetic signatures of severe storms by analyzing the hor izontal (H-component) of the Earths magnetic field. Using a moving average filter, we separated the effect of the magnetic disturbance (DP2) and the disturbance dy namo (Ddyn). Attributes of nighttime ionospheric irregularities are determined by using the rate of change of the total electron content (TEC) index (ROTI) in the longitudinal sector of 15◦W–0◦ , 15◦E–30◦E, and 30◦E–45◦E for ground-based multi ple GPS-stations and the rate of change of the electron density index (RODI) in the range of 30◦W–70◦E longitude and 50◦S–50◦N latitude for LEO satellites. In the main phase of the 17 March 2015 storm, a significant positive ionospheric storm (∆TEC maximum) occurred at Meli (245.8% enhancement) and Adis (105% enhancement) stations in the post-sunset period. On the other hand, during midnight negative ionospheric storms (∆TEC minimum: 46%-68% depletion) were observed at Dakr, Nklg, Wind, and Haro stations. The effects of the 23 June 2015 storm were more pronounced during the initial phase. In the recovery phase of the 23 June storm, negative storm effects were observed at the eastern dip latitude and western equatorial stations. In contrast, at the northern and southern mid-latitude stations, we observed positive storm effects during the night periods. The vertical drift of the ionospheric plasma probably causes nighttime TEC enhancement at mid-latitude vi stations. When the IMF-Bz is directed southward, the H-component analysis shows maximum DP2 and Ddyn current oscillations. In the main and recovery phases of the storm, this strong current oscillation drives the development of a positive ionospheric effect. Concerning the nighttime ionospheric irregularities, enhanced nighttime irregularities were observed in low latitude and equatorial region at stations YKRO, NKLG, ADIS and MAL2 during the main phase of the geomagnetic storm. The observed irregular ities were more pronounced in the western than eastern regions. These irregularities were possibly driven by the Prompt Penetration Electric Fields (PPEFs) that point east to west during the nighttime. Nighttime ionospheric irregularities were absent during the main phase of the 27 August, 7 October and 22 December 2015 storm events in all the station located at mid- latitude of the study area. In the longitudi nal sector of 15◦E - 30◦E, we obtained inhibition of irregularities in the study periods. In the case of the top-side ionosphere, we observed fluctuation of the in situ electron density during the main phases the storm in the low latitude and equatorial regions. Electron density fluctuations were seen within 15◦N and 15◦S, indicating enhanced top-side irregularities were observed in the equatorial and low-latitude regions.	en_US
dc.language.iso	en_US	en_US
dc.subject	Physics	en_US
dc.title	Characterization of the African Ionosphere Variations During Selected Geomagnetic Storms	en_US
dc.type	Thesis	en_US