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Found 11 entries in the Bibliography.
Showing entries from 1 through 11
2022 |
This study presents ionospheric responses of the mid and low-latitude region in the Europe-African longitude sector (along 30 +/- 10 deg E) to the intense geomagnetic storm of 23–31 August 2018 (SYM-Hmin = −207 nT) using the Global Ionospheric Map (GIM) and Global Positioning System (GPS) receivers data, the satellite data (SWARM, Defense Meteorological Satellite Program (DMSP), Global Ultraviolet Imager on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (GUVI/TIMED)), and Prompt Penetration Equatorial Electric Field model (PPEFM). The percentage deviation in total electron content (TEC) denoted by TEC () was used to observe the ionospheric storm effects. Dugassa, Teshome; Mezgebe, Nigussie; Habarulema, John; Habyarimana, Valence; Oljira, Asebe; Published by: Advances in Space Research Published on: YEAR: 2022   DOI: 10.1016/j.asr.2022.10.063 |
2021 |
The ionospheric responses to High-Intensity Long Duration Continuous Auroral Electrojet Activity (HILDCAA) event which happened following the CIR-driven storm were studied over the southern hemisphere mid-latitude in the African sector. The 13–15 April 2005 event was analysed to understand some of the mechanisms responsible for the ionospheric changes during HILDCAA event. The ionosonde critical frequency of F2 layer (foF2) and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) were used to analyse the ionospheric responses. The daytime increase in foF2 and TEC values were observed on 13 April 2005. The TEC and foF2 enhancement could be attributed to Large Scale Traveling Ionospheric Disturbances (LSTIDs), increase in thermospheric neutral composition changes, Prompt Penetration Electric Field (PPEF) and an expansion of Equatorial Ionization Anomaly (EIA) to the mid-latitude. Matamba, Tshimangadzo; Habarulema, John; Published by: Advances in Space Research Published on: jan YEAR: 2021   DOI: 10.1016/j.asr.2020.10.034 |
2020 |
In this study the response of ionospheric F-region to 18–21 September 2014, 19–24 January 2016, and 07–10 March 2016 CIR-driven storms in the equatorial and low-latitude region of Dugassa, Teshome; Habarulema, John; Nigussie, Melessew; Published by: Advances in Space Research Published on: YEAR: 2020   DOI: 10.1016/j.asr.2020.07.003 |
This paper focuses on unique aspects of the ionospheric response at conjugate locations over Europe and South Africa during the 7–8 September 2017 geomagnetic storm including Habarulema, John; Katamzi-Joseph, Zama; a, Dalia; Nndanganeni, Rendani; Matamba, Tshimangadzo; Tshisaphungo, Mpho; Buchert, Stephan; Kosch, Michael; Lotz, Stefan; Cilliers, Pierre; , others; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2020   DOI: 10.1029/2020JA028307 |
2016 |
This paper presents an investigation of ionospheric response to great (Dst<=\textendash350 nT) geomagnetic storms that occurred during solar cycle 23. The storm periods analyzed are 29 March to 2 April 2001, 27\textendash31 October 2003, 18\textendash23 November 2003, and 6\textendash11 November 2004. Global Navigation Satellite System, total electron content (TEC), and ionosonde critical frequency of F 2 layer (f o F 2 ) data over Southern Hemisphere (African sector) and Northern Hemisphere (European sector) midlatitudes were used to study the ionospheric responses within 15\textdegreeE\textendash40\textdegreeE longitude and \textpm 31\textdegree to \textpm 46\textdegree geomagnetic latitude. Midlatitude regions within the same longitude sector in both hemispheres were selected in order to assess the contribution of the low-latitude changes especially the expansion of equatorial ionization anomaly (EIA) also called the dayside ionospheric superfountain effect during these storms. In all storm periods, both negative and positive ionospheric responses were observed in both hemispheres. Negative ionospheric responses were mainly due to changes in neutral composition, while the expansion of the EIA led to pronounced positive storm effects at midlatitudes for some storm periods. In other cases (e.g., 29 October 2003), penetration electric fields, EIA expansion, and large-scale traveling ionospheric disturbances were found to be present during the positive storm effect at midlatitudes in both hemispheres. An increase in TEC on the 28 October 2003 was because of the large solar flare with previously determined intensity of X45 \textpm 5. Matamba, Tshimangadzo; Habarulema, John; a, Dalia; Published by: Space Weather Published on: 12/2016 YEAR: 2016   DOI: 10.1002/swe.v14.1210.1002/2016SW001516 |
We present an analysis of a regional ionospheric response during six strong storms (-200\ nT\ <=Dst<=-100\ nT) that occurred in 2012 for the geographic latitudinal coverage of 10\textdegreeS\textendash40\textdegreeS within a longitude sector of 10\textdegreeE\textendash40\textdegreeE. Although these storms occurred during the same solar activity period and were all coronal mass ejection driven, their impacts and associated features on the ionosphere have been found different due to different contributing factors to their driving mechanisms. With the exception of one case, the rest of the storm periods were characterized by positive storm effects during the main and (or) recovery phases with varying physical mechanisms including low-latitude electrodynamics, neutral composition changes, and traveling ionospheric disturbances (TIDs). The common result to all the analyzed strong storms was the presence of large-scale TIDs during the storm main phases. Using total electron content data derived from the Global Navigational Satellite System (GNSS) observations and radio occultation (RO) electron density data on a regional scale, we have attempted to investigate meridional and vertical propagation of TIDs simultaneously during the strong storms. We have showed that it is possible to identify vertical motion of TIDs using RO data in cases when equatorward TIDs, as revealed by GNSS total electron content data, are present. RO results were compared to ionosonde data, and both data sources gave vertical velocities below 100\ m/s of the associated TIDs. Habarulema, John; Katamzi, Zama; Sibanda, Patrick; Matamba, Tshimangadzo; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2016 YEAR: 2016   DOI: 10.1002/jgra.v122.110.1002/2016JA023066 |
2015 |
This paper presents a statistical analysis of ionospheric response over ionosonde stations Grahamstown (33.3\textdegreeS, 26.5\textdegreeE, geographic) and Madimbo (22.4\textdegreeS, 30.9\textdegreeE, geographic), South Africa, during geomagnetic storm conditions which occurred during the period 1996\textendash2011. Such a climatological study is important in establishing local ionospheric behavior trend which later forms a basis for accurate modeling and forecasting electron density and critical frequency of the\ F2\ layer (foF2) useful for high-frequency communication. The analysis was done using\ foF2\ and total electron content (TEC), and to identify the geomagnetically disturbed conditions, the\ Dst\ index with a storm criterion of\ Dst\ <=\ nT was used. Results show a strong solar cycle dependence with negative ionospheric storm effects following the solar cycle and positive ionospheric storm effects occurring most frequently during solar minimum. Seasonally, negative and positive ionospheric storm effects occurred most in summer (63.24\%) and in winter (53.62\%), respectively. An important finding is that only negative ionospheric storms were observed during great geomagnetic storm activity (Dst\ <=\ nT). For periods when both\ foF2\ and TEC data (from colocated ionosonde and GPS receiver stations) were available, a similar response in terms of variational trend was observed. Hence, GPS data can be used to effectively identify the ionospheric response in the absence of ionosonde data. Matamba, Tshimangadzo; Habarulema, John; McKinnell, Lee-Anne; Published by: Space Weather Published on: 09/2015 YEAR: 2015   DOI: 10.1002/swe.v13.910.1002/2015SW001218 Geomagnetic storms; ionospheric storm effects; midlatitude ionosphere |
2014 |
This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29\textendash31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18\textdegree-20\textdegree and 27\textdegree-28\textdegree were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08\textendash2.16 TECU, and 1.07\textendash2.13\ h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09\ m/s. Katamzi, Zama; Habarulema, John; Published by: Advances in Space Research Published on: 01/2014 YEAR: 2014   DOI: 10.1016/j.asr.2013.10.019 geomagnetic storm; Substorm; Total electron content (TEC); Traveling ionospheric disturbances (TIDs) |
Matamba, Tshimangadzo; Habarulema, John; McKinnell, Lee-Anne; Published by: Space Weather Published on: YEAR: 2014   DOI: https://doi.org/10.1002/2015SW001218 ionospheric storm effects; Geomagnetic storms; midlatitude ionosphere |
2013 |
In this article, the propagation characteristics of large-scale traveling ionospheric disturbances (LS TIDs) are estimated during the geomagnetic storm periods of 14\textendash16 May 2005 and 25\textendash27 September 2011 over South Africa. One and two GPS arrays have been independently considered for the storms of 15 May 2005 and 26 September 2011, respectively. The average periods of dominant modes (≈ 2.5\textendash3.5h) in the time series data were determined by applying wavelet analysis on both ionosonde and GPS data. The consideration of diurnal GPS total electron content (TEC) variability from receivers along three different longitude sectors showed a time shift in TEC enhancement with increasing latitude, the first indication of equatorward motion of the traveling ionospheric disturbances (TIDs). The statistical method (based on GPS radio interferometry) employed shows that these TIDs were mostly propagating nearly equatorward (for both storm periods), which is consistent with the existing literature about storm-induced TIDs. On storm days, TID horizontal velocities have been determined in the range of ≈200\textendash500m/s. The analysis of diurnal TEC response from different stations confirmed that the positive storm effect observed on 15 May 2005 was a result of the large-scale TIDs of wavelength ≈4000 km. On the other hand, the estimated wavelengths of LS TIDs on 26 September 2011 were ≈2400\textendash3400km between 10 and 17 UT. A time lag is observed between the times at which enhancements in TEC, ionosonde foF2, and hmF2 data are revealed, and this has been attributed to the passage of the TID. Habarulema, John; Katamzi, Zama; McKinnell, Lee-Anne; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2013 YEAR: 2013   DOI: 10.1002/2013JA018997 characteristics of large scale TIDs; Geomagnetic storms; ionospheric irregularities |
The solar wind effects on the Earth\textquoterights environment are studied for their basic scientific values and crucial practical impacts on technological systems. This paper reports results of Total Electron Content (TEC) changes during two successive ionospheric storms of 7\textendash12 November 2004 using GPS data derived from dual frequency receivers located at African equatorial and midlatitudes. In the geographic coordinate system, equatorial TEC variability is considered over Libreville (0.36\textdegreeN, 9.67\textdegreeE), Gabon and Mbarara (0.60\textdegreeS, 30.74\textdegreeE), Uganda. TEC over midlatitude stations Sutherland (32.38\textdegreeS, 20.81\textdegreeE) and Springbok (29.67\textdegreeS, 17.88\textdegreeE), South Africa are analysed. The analysis of the storm time ionospheric variability over South Africa was undertaken by comparing the critical frequency of the F2 layer (foF2) and the peak height of the F2 layer (hmF2) values obtained from Grahamstown (33.30\textdegreeS, 26.53\textdegreeE) and Madimbo (22.4\textdegreeS, 30.9\textdegreeE) ionosonde measurements. During the analysed storm period it is observed that GPS TEC for midlatitudes was depleted significantly with a corresponding depletion in foF2, due to the reduction in GUVI O/N2 ratio as observed from its global maps. Over the equatorial latitudes, positive storm effects are more dominant especially during the storm main phase. Negative storm effects are observed over both mid and equatorial latitudes during the recovery phase. A shift in equatorial TEC enhancement (from one GPS station to another) is observed during magnetic storms and has been partially attributed to passage of Travelling Ionospheric Disturbances (TIDs). Magnetometer data over the International Real-time Magnetic Observatory Network (intermagnet) station, Addis Ababa, AAE (9.03\textdegreeN, 38.77\textdegreeE) has been used to help with the explanation of possible causes of equatorial ionospheric TEC dynamics during the analysed magnetic storm period. Habarulema, John; McKinnell, Lee-Anne; a, Dalia; Zhang, Yongliang; Seemala, Gopi; Ngwira, Chigomezyo; Chum, Jaroslav; Opperman, Ben; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 09/2013 YEAR: 2013   DOI: 10.1016/j.jastp.2013.05.008 African equatorial and midlatitude TEC dynamics; Magnetic storms; TIDs |
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