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foF2 Long-Term Trend at a Station Located near the Crest of the Equatorial Ionization Anomaly

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Document pages: 11 pages

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, areanalysed taking into account geomagnetic activity, increasing greenhouse gasesconcentration and Earth’s magnetic field secular variation. After filteringsolar activity effect using F10.7 as a solar activity proxy, we determined therelative residual trends slopes α values for three different levels of geomagnetic activity. For example, at 1200LT, the value of α goes from &#450.27 year for very magnetically quiet days to -0.19 year for magneticallyquiet days and to -0.13 year for all days. It appears from the slopes α obtained, that they increase with thelevel of geomagnetic activity and their negative values are qualitativelyconsistent with the expected decreasing trend due to the increase in greenhousegases concentration but are greater than 0.003 year which would result from a20 increase in CO2 emissions which actually took place during theanalysis period. Regarding Earth’s magnetic field magnitude, B secularvariation and the dip equator secular movement, Dakar station is located near the crest of theequatorial ionization anomaly, Earth’s magnetic field magnitude, B decreasesthere and the trough approaches the position of Dakar during the period ofanalysis. These two phenomena induce a decrease in foF2 which is in agreementwith the decreasing trend observed at this station.

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