foF2 Long Term Trends at Ouagadougou Station

A trough station (Ouagadougou station) of African Equatorial Ionization Anomaly sector foF2 long term trends are carried out after the elimination of solar cycle long term variation part. For this part, foF2 is expressed as a third degree polynomial function of Rz. We analyzed diurnal, seasonal and annual foF2 long term trends during 30 years covering the period 1966-1996. Diurnal trend variation showed positive hourly trend at the morning (slope maximum value at 0400 LT: + 1.5 x 10-3 per year) and at night (slope maximum value at 2200 LT: + 0.7 x 10-3 per year). During night and morning times well correlation is observed between foF2 and Ap. The absolute maximum trend is observed at 1900 LT (+ 2.5 x 10-3 per year). Seasonal variation at 1900 LT exhibited for each season positive trend except during summer where negative trend was observed (-0.0472 per year). At equinoxes, there is no asymmetry and foF2 trend is + 0.0412 per year. Annual investigation showed that from 1966 to 1981 Ap and foF2 present the same sense variation while from 1981 to 1966 it is the reverse. At 0400 LT, between 1966 and 1981 relative foF2 presents positive trend (+5.4 x 10-3 per year) and between 1981 and 1996, it shows negative trend (- 5.3 x 10-3 per year). At 1900 LT, for the 30 years involved, relative foF2 shows strong negative trend (- 6.5x 10-3 per year).