Bibliography

Effect of moderate geomagnetic storms on equatorial plasma bubbles over eastern Africa in the year 2012: Evolution and electrodynamics

Equatorial plasma bubbles (EPBs) are common features of the equatorial and low-latitude ionosphere and are known to cause radio wave scintillation which leads to the degradation of communication and navigation systems. Although these structures have been studied for decades, a full understanding of their evolution and dynamics remains important for space weather mitigation purposes. In this study, we present cases of EPBs occurrences around April and July 2012 geomagnetic storm periods over the African equatorial sector. The EPBs were observed from the Communications/Navigation Outage Forecasting System (C/NOFS) and generally correlated well to the ionospheric irregularities observed from the Global Positioning System total electron content (GPS-TEC) measurements (rate of TEC change, ROT). This study revealed that the evolution of the EPBs during moderate storms is controlled by the strength of the daytime equatorial electrojet (EEJ) currents regardless of the strength of the equatorial ionization anomaly (EIA), the latter is observed during the July storm case in particular. These effects were more evident during the main and part of the early recovery phases of the geomagnetic storm days considered. However, the evening hours TEC gradients between regions of the magnetic equator and ionization crests also played roles in the existence of ionospheric irregularities.

Giday, Nigussie; Katamzi-Joseph, Zama; Stoneback, Russell;

Published by: Advances in Space Research      Published on: 04/2020

YEAR: 2020     DOI: 10.1016/j.asr.2020.01.013

C/NOFS; Equatorial electrojets; equatorial plasma bubbles

Ionospheric response at conjugate locations during the 7—8 September 2017 geomagnetic storm over the Europe-African longitude sector

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

Assessing ionospheric response during some strong storms in solar cycle 24 using various data sources

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

Traveling ionospheric disturbances observed at South African midlatitudes during the 29--31 October 2003 geomagnetically disturbed period

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)

Estimating the propagation characteristics of large-scale traveling ionospheric disturbances using ground-based and satellite data

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 f_oF₂, and h_mF₂ 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