Throughout the solar cycle and predominantly during the declining phase, Stream Interaction Regions (SIRs) drive space weather on Earth. SIRs occur when the Sun’s rotation aligns a fast solar wind stream behind a slow solar wind stream. Both fast wind and slow wind are compressed and heated, forming a pressure ridge driven by the dynamic pressure of the fast wind. In the frame advecting with the SIR, the high pressure region is bound by a forward wave, which propagates away from the Sun, and reverse wave which propagates sunwards. The pressure waves steepen into shocks with increasing heliospheric distance, the shocks usually form beyond Earth’s orbit. Located between the waves, the stream interface is a tangential discontinuity separating streams that were originally fast from slow. While the general mechanism for the formation and evolution of SIRs is relatively well known, the implications of the 3D structure in the inner heliosphere have not been well understood, in part due to the sparsity of in situ observations outside of the ecliptic plane. In this dissertation, I have used the heliospheric adaptation of the Lyon-Fedder- Mobarry (LFM-helio) MHD model to simulate both idealized and realistic SIR structures in order to validate the model against in situ measurements and to elucidate which characteristics of the solar wind influence the evolution of SIRs. The LFM-helio is shown to accurately reproduce the solar wind conditions at various heliospheric distances. The simulations produced SIRs which agree with in situ observations. The simulations were used to show that the large scale shape of high speed streams driving SIRs affect the amount of heating, compression, and flow deflection. Further, for even small latitudinal separations, SIR evolution depends on the latitudinal structure of the High Speed Stream driving the SIR. Increasing the temperature at the inner boundary of the LFM-helio results in a solar wind that is globally faster and that produces SIRs exhibiting less compressive heating. Increasing the magnetic field strength uniformly at the inner boundary has an effect on the dynamical evolution SIRs whereas increasing the magnetic field strength in proportion to the solar wind speed latitudinally compresses the extent of the band of slow wind, modifying the global structure of the heliosphere.

Les ceintures de radiation correspondent à la région de la magnétosphère dans laquelle se trouvent les particules de hautes énergies. Le couplage entre le vent solaire et la magnétosphère donne lieu à des variations des flux de particules sur plusieurs ordres de grandeurs. L’objectif de cette thèse est d’observer et caractériser ces variations de flux d’électrons au passage de différents types d’événements tels que les régions d’interaction en co-rotation (CIRs) et les éjections de masse coronale interplanétaires (ICMEs). Pour cela, nous avons traité et analysé les données de plusieurs types: paramètres du vent solaire, indices géomagnétiques et flux d’électrons dans les ceintures de radiation. Dans les trois premiers chapitres, nous rendons compte de la complexité de l’environnement spatial Terrestre et présentons les différentes données utilisées. Les travaux de thèse sont ensuite organisés en quatre chapitres. Premièrement, nous utilisons les mesures des satellites NOAA-POES afin de caractériser les flux d’électrons dans les ceintures. Nous étudions ensuite les différences de variations de flux causées par les CIRs et les ICMEs en fonction de l’énergie des électrons et du paramètre L*. Après avoir montré le fort lien entre les intensités d’orages magnétiques et les variations de flux, nous nous focalisons sur les ICMEs et la variabilité des orages qu’elles causent. Enfin, nous insistons sur l’importance des enchaînements d’événements. Après avoir quantifié la forte tendance qu’ont les ICMEs à former des séquences, nous réalisons une étude statistique sur les orages qu’elles causent, puis trois études de cas afin d’illustrer leurs effets sur les ceintures. / The radiation belts are the toroidal region within the inner magnetosphere where high energetic particles are located. The coupling between the solar wind and the magnetosphere leads to strong variations of particle fluxes that can therefore increase or decrease over several orders of magnitude. The aim of this thesis is to observe and characterize the variations of fluxes during the crossing of several types of events originating from the sun such as Corotating Interaction Regions (CIRs) and Interplanetary Coronal Mass Ejections (ICMEs). To do so, we processed and analyzed the data of various types : solar wind parameters, geomagnetic indices, and electron fluxes within the radiation belts. In the three first chapters, we report on the complexity of the Terrestrial space environment and we present the Solar-Terrestrial system and the data used. Then, our work is organized around four chapters. First, we characterized the electron fluxes within the radiation belts as measured by the NOAA-POES spacecrafts. Then, we studied the difference between the variations of fluxes caused by the CIRs and the ICMEs depending on the energy and the L* parameter. After establishing strong links between the intensity of magnetic storms and the variations of fluxes, we focused on the ICMEs and the variability of the related magnetic storms. Eventually, we emphasized the importance of the sequences of events. After quantifying the trend of the ICMEs to form sequences, we performed a statistical study on the magnetic storms caused by such sequences. Finally three study cases were performed in order to illustrate the various possible effects on the radiation belts.