West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998

Abstract

Abstract. This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only foF2 exhibits annual, winter and semiannual anomaly. foF2 seasonal variation has permitted us to identify and characterize solar events effects on F2 layer in this area. In fact (1) during quiet geomagnetic condition foF2 presents winter and semiannual anomalies asymmetric peaks in March/April and October. (2) The absence of winter anomaly and the presence of equinoctial peaks are the most visible effects of fluctuating activity in foF2 seasonal time profiles. (3) Solar wind shock activity does not modify the profile of foF2 but increases ionization. (4) The absence of asymmetry peaks, the location of the peaks in March and October and the increase of ionization characterize recurrent storm activity. F1 layers shows increasing trend from cycle 20 to cycle 21. Moreover, E layer parameters seasonal variations exhibit complex structure. It seems impossible to detect fluctuating activity effect in E layer parameters seasonal variations but shock activity and wind stream activity act to decrease E layer ionization. It can be seen from Es layer parameters seasonal variations that wind stream activity effect is fairly inCorrespondence to: F. Ouattara (fojals@yahoo.fr) dependent of solar cycle. E and Es layers critical frequencies and virtual heights diurnal variations let us see the effects of the greenhouse gases in these layers.

Studying the variability in the diurnal and seasonal variations in GPS total electron content over Nigeria

“…During sunrise, the magnetic flux tubes again filled up because of their small volume, resulting in a sudden increase in ionization due to increasing thermospheric temperatures during sunrise (Oron et al, 2013). The observed nighttime GPS TEC enhancement could be attributed to the tidal winds, which blow the ionization across the geomagnetic field.…”

Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam

“…This is related to winter maximum of O atoms, implying the relative increase of light gases above the winter hemisphere (Scialom, 1974), due to dynamic influences in the thermosphere (Rishbeth and Müller-Wodarg, 2006). Ouattara et al (2009) propose to explain the absence of the winter anomaly during cycle 20 by the influence of fluctuating wind stream activity.…”

“…The difference in the correlation coefficients from one sunspot cycle to another can be explained by changes in the solar cycle intensity (Balan et al, 1993). Ouattara et al (2009) found for Ouagadougou, located at the magnetic equator in the Northern Hemisphere, a good correlation between the sunspot number and foF2, foF1, and h F1, but no correlation for foE, h F2 and h E. The absence of correlation between the sunspot number and foE at the equator can be explained by the existence of the equatorial electrojet, which drives instabilities and generates strong plasma waves which strongly affect the electron density (Farley, 2009). …”

“…We use hourly values at full hours of critical frequencies foF2, foF1, foE and foEs and virtual heights h F2, h F1, h E, h Es. The ionosonde data were continuously recorded by three different ionospheric vertical sounders: the IRX-Hungarian (1962-1966, the AIC-Russian (1967-1994, the IPS71-Australian (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002).…”

“…-The long term variations observed by ionosonde located in different regions were previously analyzed by Elias and Ortiz de Adler (2006), Bremer (2008) and Ouattara et al (2009). Three factors were proposed to explain the long term variation (Lastovicka et al, 2006;Elias, 2009): (1) green house gases (Bremer, 2008), (2) changes in the Earth's magnetic field (Elias and Ortiz de Adler, 2006;Cnossen and Richmond, 2008) and (3) geomagnetic activity.…”