Statistical study of the equatorial F2 layer critical frequency at Ouagadougou during solar cycles 20, 21 and 22, using Legrand and Simon's classification of geomagnetic activity

International audienceThis paper presents the statistical analysis of the diurnal variations of the F layer at the equatorial station of Ouagadougou (Lat: 12.4 N; Long: 358.5 E; dip: 5.9 ) from 1966 to 1998 (=> ~11 680 days). We consider three main factors of variability: (1) the season (spring, summer, autumn and winter), (2) the phase of the sunspot cycle (ascending, maximum, descending and minimum) and (3) the geomagnetic activity classified by Legrand and Simon in four groups: slow solar wind, high solar wind streams, fluctuating solar wind and shock activity. We easily identify the influence of the solar wind speed and shock activity on the diurnal pattern of the F layer. Shock and recurrent activities tend to enhance or diminish the morning or afternoon maximum of the F2 layer critical frequency. The difference of the diurnal foF2 variation during the increasing and decreasing phases of the sunspot solar cycle is explained by different solar wind regimes. The slow solar wind dominates during the increasing phase of the sunspot cycle and the fluctuating solar wind dominates during the decreasing phase of the sunspot cycle. This paper demonstrates that it is possible using a large database, to bring up significant morphologies of the diurnal variation of the foF2 critical frequency as a function of (1) different solar events such as quiet solar wind, fluctuating wind, recurrent high stream wind and Coronal Mass Ejections (CMEs); (2) solar cycle phases and (3) seasons. It is an approach directly connecting the critical frequency of the F2 layer to the solar parameters

A COMPARATIVE STUDY OF SEASONAL AND QUIETTIME foF2 DIURNAL VARIATION AT DAKAR AND OUAGADOUGOU STATIONS DURING SOLAR MINIMUM AND MAXIMUM FOR SOLAR CYCLES 21-22

A statistical study of quiet time foF2 diurnal variation of two West Africa stations (Dakar and Ouagadougou) is examined through seasons and during solar minimum and maximum phases. It is shown that during solar minimum and for all seasons both stations foF2 exhibit the same variability with more and less deep trough between 1200 LT and 1400 LT. foF2 profiles are afternoon predominance profiles except during winter and for Dakar station where the profile is morning predominance peak. During solar maximum, foF2 profiles show different behavior only for spring and summer where Dakar foF2 profiles are plateau profile and dome profile, respectively. For these seasons Ouagadougou profiles are morning predominance profile and noon bite out profile, respectively. At daytime there is more ionosphere at Dakar station than Ouagadougou at all seasons and for the solar cycle phases involved

Primitives de sécurité à base de mémoires magnétiques

Magnetic memories (MRAM) are one of the emerging non-volatile memory technologies that have experienced rapid development over the past decade. One of the advantages of this technology lies in the varied fields of application in which it can be used. In addition to its primary function of storing information, MRAM is nowadays used in applications such as sensors, RF receivers and hardware security. In this thesis, we are interested in the use of MRAMs in the design of elementary hardware security primitives. Initially, an exploration in the design of TRNG (True Random Number Generator) based on STT-MRAM (Spin Transfert Torque MRAM) type memories was carried out with the aim of producing a demonstrator and proving its effectiveness for secure applications. Random extraction methods in STT and TAS (Thermally Assisted Switching) memories are presented. We have thus evaluated these magnetic memories within the framework of TRNGs but also for the generation of PUFs (Physically Unclonable Functions) on physical devices.Les mémoires magnétiques (MRAM) font partie des technologies de mémoires non volatiles émergentes ayant connu un développement rapide cette dernière décennie. Un des avantages de cette technologie réside dans les domaines d’applications variées dans lesquelles elle peut intervenir. En plus de sa fonction principale de stockage d’information, la MRAM est utilisée de nos jours dans des applications de type capteurs, récepteur RF et sécurité matérielle. Dans cette thèse, nous nous sommes intéressés à l’utilisation des MRAM dans la conception des primitives de sécurité matérielle élémentaires. Dans un premier temps, une exploration dans la conception de TRNG (True Random Number Generator) basée sur des mémoires de type STT-MRAM (Spin Transfert Torque MRAM) a été menée dans le but de réaliser un démonstrateur et de prouver son efficacité pour les applications sécurisées. Les méthodes d’extraction d’aléa dans les mémoires STT et TAS (Thermally Assisted Switching) sont présentées. Nous avons ainsi évalué ces mémoires magnétiques dans le cadre des TRNG mais également pour la génération de PUF (Physically Unclonable Functions) sur des dispositifs physiques

Relationship between geomagnetic classes’ activity phases and their occurrence during the sunspot cycle

Four well known geomagnetic classes of activity such as quiet days activity, fluctuating activity, recurrent activity<br />and shock activity time occurrences have been determined not only by using time profile of sunspot number<br />Rz but also by using aa index values.<br />We show that recurrent wind stream activity and fluctuating activity occur in opposite phase and slow solar wind<br />activity during minimum phase and shock activity at the maximum phase.<br />It emerges from this study that fluctuating activity precedes the sunspot cycle by π/2 and the latter also precedes<br />recurrent activity by π/2. Thus in the majority the activities do not happen at random; the sunspot cycle starts<br />with quiet days activity, continues with fluctuating activity and during its maximum phase arrives shock activity.<br />The descending phase is characterized by the manifestation of recurrent wind stream activity

Magnetic Memory based secure devices

National audienceMagnetic memory (MRAM) never stops attracting both industry and academy for a wide range of applications. With its non-volatility, high density, ultra-low static power, radiation robustness, and easy integration with CMOS, MRAM is showing a good capability in secure applications. This paper aims at introducing the strong potential of using MRAM for secure devices

Variability of CODG TEC and IRI 2001 total electron content (TEC) during IHY campaign period (21 March to 16 April 2008) at Niamey under different geomagnetic activity conditions

International audienceIRI 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 betwen CODG TEC maps and IRI 2001 TEC shows the overestimation of IRI 2001 model. The overestimaion 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 periof, 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