Long-term trend of foF2 at a West-African equatorial station linked to greenhouse gases increase and dip equator secular displacement

DOUA A. GNABAHOU; ANA G. ELIAS; FREDERIC OUATTARA

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Año: 2013 vol. 118 p. 3909 - 3913

0148-0227

Long-term variability of foF2 at Ouagadougou station (12.4°N, 358.5°E, dip: 1.45°), a West-African equatorial station, is studied analyzing an annual mean data series at 12 LT for the period 1966-1998. After filtering the solar activity effect using Rz as a solar activity proxy, a downward trend of -0.015 MHz/year is obtained, that is a ~5% decrease during the period of 33 years here considered, equivalent to a ~0.2%/year. The downward trend is qualitatively consistent with a decreasing trend expected from increasing greenhouse concentration gases but greater than the ~0.003%/year that would result from the 20% increase in CO2 that actually took place during the period of analysis. The foF2 decreasing trend is not in agreement with the trend expected from the secular variation of the dip angle at the location of Ouagadougou, but here, an additional mechanism is considered, that is the secular movement of the dip equator toward Ouagadougou. This implies an approaching of the trough of the equatorial ionization anomaly, EIA, and thus an foF2 decrease at Ouagadougou that is qualitatively in agreement with the observed trend.