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Zerbo J.L.,Bobo-Dioulasso Polytechnic University | Zerbo J.L.,CNRS Physics Laboratory | Amory Mazaudier C.,CNRS Physics Laboratory | Ouattara F.,Ecole Normale Superieure Of Luniversite Of Koudougou | Richardson J.D.,Center for Space Research
Annales Geophysicae | Year: 2012

We examined solar activity with a large series of geomagnetic data from 1868 to 2009. We have revisited the geomagnetic activity classification scheme of Legrand and Simon (1989) and improve their scheme by lowering the minimum Aa index value for shock and recurrent activity from 40 to 20 nT. This improved scheme allows us to clearly classify about 80% of the geomagnetic activity in this time period instead of only 60% for the previous Legrand and Simon classification. © Author(s) 2012.


Ouattara F.,Ecole Normale Superieure Of Luniversite Of Koudougou | Fleury R.,ENST Bretagne Technopole Brest Iroise
Scientific Research and Essays | Year: 2011

IRI 2001 model prediction is compared to custom orthotic design group total electron content (CODG TEC) maps prediction at Niamey during several geomagnetic (quiet, fluctuating and shock days) conditions for the period of IHY campaign. Independently of geomagnetic conditions, the qualitative comparison between CODG TEC maps and IRI 2001 TEC shows the overestimation of IRI 2001 model. The overestimation of CODG TEC maps at Niamey by IRI model is also shown by examining quantitative methods (relative deviation module means (rdmm) and percentage deviation) results. The quality of IRI prediction, that is, the amplitude of estimation depends on geomagnetic condition and month. In fact, rdmm values of March and April for quiet day periods respectively are 0.53 and 0.41. During fluctuating period, rdmm values are 0.35 in March and 0.39 in April. When act CMEs, rdmm value is 0.67; thus the work shows on one hand the necessity to improve IRI model and on the other hand to study the effect of each disturb solar event separately. © 2011 Academic Journals.


Ouattara F.,Ecole Normale Superieure Of Luniversite Of Koudougou | Gnabahou D.A.,Direction Regional du Center Ouest | Amory Mazaudier C.,University Pierre and Marie Curie
International Journal of Geophysics | Year: 2012

We analyse the variability of foF2 at two West Africa equatorial ionization anomaly stations (Ouagadougou and Dakar) during three solar cycles (from cycle 20 to cycle 22), that is, from 1966 to 1998 for Ouagadougou and from 1971 to 1997 for Dakar. We examine the effect of the changing levels of solar extreme ultraviolet radiation with sunspot number. The study shows high correlation between foF2 and sunspot number (Rz). The correlation coefficient decreases from cycle 20 to cycle 21 at both stations. From cycle 21 to cycle 22 it decreases at Ouagadougou station and increases at Dakar station. The best correlation coefficient, 0.990, is obtained for Dakar station during solar cycle 22. The seasonal variation displays equinoctial peaks that are asymmetric between March and September. The percentage deviations of monthly average data from one solar cycle to another display variability with respect to solar cycle phase and show solar ultraviolet radiation variability with solar cycle phase. The diurnal variation shows a noon bite out with a predominant late-afternoon peak except during the maximum phase of the solar cycle. The diurnal Ouagadougou station foF2 data do not show a significant difference between the increasing and decreasing cycle phases, while Dakar station data do show it, particularly for cycle 21. The percentage deviations of diurnal variations from solar-minimum conditions show more ionosphere during solar cycle 21 at both stations for all three of the other phases of the solar cycle. There is no significant variability of ionosphere during increasing and decreasing solar cycle phases at Ouagadougou station, but at Dakar station there is a significant variability of ionosphere during these two solar-cycle phases. © 2012 Frédéric Ouattara et al.


Gnabahou D.A.,Ecole Normale Superieure Of Luniversite Of Koudougou | Elias A.G.,CONICET | Elias A.G.,National University of Tucuman | Ouattara F.,Ecole Normale Superieure Of Luniversite Of Koudougou
Journal of Geophysical Research: Space Physics | Year: 2013

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/yr is obtained, that is a ∼5% decrease during the period of 33 years here considered, equivalent to a ∼0.2%/yr. The downward trend is qualitatively consistent with a decreasing trend expected from increasing greenhouse gas concentration but greater than the ∼0.003%/yr that would result from the 20% increase in CO2 that actually took place during the period of analysis. The foF 2 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 and thus an foF2 decrease at Ouagadougou that is qualitatively in agreement with the observed trend. © 2013. American Geophysical Union. All Rights Reserved.

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