TITLE:
foF2 Long-Term Trend at a Station Located near the Crest of the Equatorial Ionization Anomaly
AUTHORS:
Doua Allain Gnabahou, Sibri Alphonse Sandwidi, Frédéric Ouattara
KEYWORDS:
Geomagnetic Activity, Long-Term Trend, foF2, Dip Equator
JOURNAL NAME:
International Journal of Geosciences,
Vol.11 No.8,
August
17,
2020
ABSTRACT: Critical frequency foF2 long-term trends at Dakar station (14.4°N,
342.74°E) located near the crest of the equatorial ionization anomaly EIA, are
analysed taking into account geomagnetic activity, increasing greenhouse gases
concentration and Earth’s magnetic field secular variation. After filtering
solar activity effect using F10.7 as a solar activity proxy, we determined the
relative residual trends slopes α values for three different levels of geomagnetic activity. For example, at 1200
LT, the value of α goes from ǂ.27%/year for very magnetically quiet days to -0.19%/year for magnetically
quiet days and to -0.13%/year for all days. It appears from the slopes α obtained, that they increase with the
level of geomagnetic activity and their negative values are qualitatively
consistent with the expected decreasing trend due to the increase in greenhouse
gases concentration but are greater than 0.003%/year which would result from a
20% increase in CO2 emissions which actually took place during the
analysis period. Regarding Earth’s magnetic field magnitude, B secular
variation and the dip equator secular movement, Dakar station is located near the crest of the
equatorial ionization anomaly, Earth’s magnetic field magnitude, B decreases
there and the trough approaches the position of Dakar during the period of
analysis. These two phenomena induce a decrease in foF2 which is in agreement
with the decreasing trend observed at this station.