African Ionosphere Research Articles

Total Electron Content Variability in the African Ionosphere Observed during Ascending and Decaying Geomagnetic Storms

Total Electron Content Variability in the African Ionosphere Observed during Ascending and Decaying Geomagnetic Storms

Plasma re-distribution in the African low-latitude ionosphere during intense geomagnetic storms

Intense geomagnetic storms offer opportunity to understand ionospheric response to space weather events. Using Total Electron Content (TEC) data from stations along the east African sector, the two most intense storms during the 24th solar cycle, with similarly occurrence season and time were studied. We observe that ionospheric effect during the main phase is not a function of the severity of the storm, whereas the more intense storm shows greater influence on the African ionosphere during the recovery phase. Plasma movement within the equatorial ionization anomaly (EIA) was evident particularly during the recovery phase, especially during the 2015 event. For both storms, the nighttime/early morning ionospheric effect is more pronounced than the daytime effects across all stations.
 

Pattern of Latitudinal Distribution of Ionospheric Irregularities in the African Region and the Effect of March 2015 St. Patrick's Day Storm

AbstractThis paper investigates the latitudinal distribution of quiet and storm time irregularities over the African ionosphere in the month of March 2015. The average rate of change in total electron content (TEC) index (ROTIave) calculated from Global Positioning System data is used as a proxy for the irregularities. The result during the quiet condition shows that irregularities are mostly observed between 19:00 and 00:00 LT regardless of the hemisphere. Its appearance in the Southern Hemisphere is earlier, though with less severity mainly around the equatorward edge of the equatorial anomaly peak. The peak of its development occurred at 21:00 LT, as it is observed in all the latitudes except those outside the equatorial region. The strength is found to be most severe at ∼12° magnetic latitude (up to 1.10 TECU/min.) in the south. Beyond ∼18° magnetic latitude, it is rarely noticed in the south. However, it is not observed around this latitude in the north, indicating a major hemispheric asymmetry in terms of the latitudinal boundary between the Northern and Southern Hemispheres. Furthermore, its disappearance is found to be most rapid around the poleward verge of the equatorial anomaly region particularly in the Southern Hemisphere. In contrast to quiet time observations, irregularities were absent in all latitudes during the storm days considered. This can be attributed to the local time of the storm's onset and the possible imposition of westward electric fields in the dusk period.

Mapping the East African Ionosphere Using Ground-based GPS TEC Measurements

The East African ionosphere (3°S-18°N, 32°E-50°E) was mapped using Total Electron Content (TEC) measurements from ground-based GPS receivers situated at Asmara, Mekelle, Bahir Dar, Robe, Arbaminch, and Nairobi. Assuming a thin shell ionosphere at 350 km altitude, we project the Ionospheric Pierce Point (IPP) of a slant TEC measurement with an elevation angle of >10° to its corresponding location on the map. We then infer the estimated values at any point of interest from the vertical TEC values at the projected locations by means of interpolation. The total number of projected IPPs is in the range of 24-66 at any one time. Since the distribution of the projected IPPs is irregularly spaced, we have used an inverse distance weighted interpolation method to obtain a spatial grid resolution of 1°×1° latitude and longitude, respectively. The TEC maps were generated for the year 2008, with a 2 hr temporal resolution. We note that TEC varies diurnally, with a peak in the late afternoon (at 1700 LT), due to the equatorial ionospheric anomaly. We have observed higher TEC values at low latitudes in both hemispheres compared to the magnetic equatorial region, capturing the ionospheric distribution of the equatorial anomaly. We have also confirmed the equatorial seasonal variation in the ionosphere, characterized by minimum TEC values during the solstices and maximum values during the equinoxes. We evaluate the reliability of the map, demonstrating a mean error (difference between the measured and interpolated values) range of 0.04-0.2 TECU (Total Electron Content Unit). As more measured TEC values become available in this region, the TEC map will be more reliable, thereby allowing us to study in detail the equatorial ionosphere of the African sector, where ionospheric measurements are currently very few.

An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using global positioning system (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the TEC. During this storm, two TEC enhancements were observed at low- and mid-latitudes: the first enhancement was observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, while the second TEC enhancement is associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show response features that differ from those of the TEC during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers may have existed, i.e., the westward electric field and equatorward neutral wind effects.

Developing an ionospheric map for South Africa

Abstract. The development of a map of the ionosphere over South Africa is presented in this paper. The International Reference Ionosphere (IRI) model, South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were combined within their own limitations to develop an accurate representation of the South African ionosphere. The map is essentially in the form of a computer program that shows spatial and temporal representations of the South African ionosphere for a given set of geophysical parameters. A validation of the map is attempted using a comparison of Total Electron Content (TEC) values derived from the map, from the IRI model, and from Global Positioning System (GPS) measurements. It is foreseen that the final South African ionospheric map will be implemented as a Space Weather product of the African Space Weather Regional Warning Centre.

An analysis of automatically scaled F1 layer data over Grahamstown, South Africa

This paper describes an analysis of automatically scaled F1 layer data over Grahamstown, South Africa (33.3°S, 26.5°E). Anapplication for real time raytracing through the South African ionosphere was identified, and for this application real time evaluation of the electron density profile is essential. Raw real time virtual height data are provided by a Lowell Digisonde (DPS), which employs the automatic scaling software, ARTIST whose output includes the virtual-to-real height data conversion. Experience has shown that there are times when the raytracing performance is degraded because of difficulties surrounding the real time characterisation of the Fl region by ARTIST. The purpose of this investigation is to establish the extent of the problem, the times and conditions under which it occurs, with a view to formulating remedial alternative strategies, such as predictive modelling.