Long-term trend of foF2 at a West African equatorial station

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

Buenos Aires

Workshop; 7th Workshop on Long-Term Changes and Trends in the Atmosphere; 2012

FACEYT - UNT

In the present work, the long-term variability of foF2 at Ouagadougou station (lat: 12.4◦N; long: 358.5◦E; dip: +1.45), which is a West African equatorial station, is analyzed for the period 1966-1998. The annual mean data series was filtered using Rz as a solar activity proxy, and also adding to Rz the aa index as a geomagnetic activity measure. Both filtered series behave very similarly. A downward overall trend is noticed of -0.015 MHz/year, which means a 5 % decrease during the whole period of 32 years here considered. The downward trend is qualitatively consistent with a decreasing trend expected from increasing greenhouse concentration gases, but greater than the ~ -0.003 expected from a 20% increase in CO2 during the period considered. The foF2 decreasing trend is also qualitatively in agreement with the trend expected from the secular variation of the dip angle at the location of Ouagadougou. Here, an additional mechanism is playing its role, and it is the secular movement of the dip equator, that in our case means an approach of the trough of the equatorial ionization anomaly, which also would induce an additional decrease in foF2.