Analysis of the Factors Affecting Ionospheric Total Electron Content in East Africa and Middle East
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Date
2021-11-29
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Addis Ababa University
Abstract
The low latitude and equatorial ionospheric total electron content (TEC) variations
are investigated using dual frequency GPS TEC data taken from 7 GPS stations in
which 6 are found in East Africa and one is found in Saudi Arabia in the year of
2015. This GPS TEC data was used to study the diurnal, seasonal, geomagnetic and
latitudinal variations of ionospheric TEC at these GPS stations as insu_cient research
results of ionospheric variations are available for these areas. The results of the analysis
showed that the ionospheric TEC undergoes diurnal, seasonal, geomagnetic (quiet and
disturbed day) and latitudinal variations. With regard to the diurnal variation, the
TEC value shows minimum at predawn and gradual increase with time of the day
attaining a maximum in the afternoon and a gradual decrease after sunset. This
is the result of photo ionization of the atmosphere due to the increased intensity of
solar radiation during day. On the other hand during night electron loss processes
(ion-electron recombination and electron attachment) dominate and the TEC value is
decreased. The TEC value in March shows a very rapid decrease after sunset due to the
high recombination rate that is proportional to the square of the high electron density
in March. Moreover, the night time TEC value shows a secondary minima maxima
near dawn which may be due to the Counter Electrojet (CEJ). The TEC value in the
solstice months of June and December don't show plateau and secondary maxima. It
simply increase till noon and then decreases slowly during afternoon and during night.
The seasonal variation is caused by the relative position of the Earth with the
sun which changes the solar zenith angle. The greatest TEC value occurred in the
equinoctial month of March and the least occurred during the winter solstice month
of December and intermediate TEC value is recorded in summer solstice month of
June. The e_ects of geomagnetic storms on TEC values have been also considered
in this study. The result reveals that the storm day TEC value is greater than the
quiet day TEC value. This is due to the fact that high amount of solar particles reach
the earth and there is more ionization during the storm period. The TEC value also
vary with latitude. The highest TEC value is obtained for stations that are closer to
the geomagnetic equator (MOIU in Kenya) in the southern hemisphere. This may be
the result of the occurrence of highly radiation of the sun and the DEBK station in
Ethiopia located around EIA crest region is due to the fountain e_ect. The least value
of TEC is observed for stations far from the geomagnetic equator (SOLA in Saudi
Arabia) which is located beyond the EIA region. Moreover, TEC value of January 3,
2015 (at perihelion) is greater than that of the July 3, 2015 (aphelion), 2015. For the
future more research need on the perihelion and aphelion cases of ionospheric TEC.
Description
Keywords
Tec, Ionosphere, Diurnal Variation, Seasonal Variation, Latitudinal, Variation, Geomagnetic Storm Variation, Equatorial Ionization Anomaly, East African, Low Latitude /Equatorial Region, Fountain Effect