Study Of Solar Energetic Electrons Propagation Based On Source And Diffusion Mechanism

Solar energetic particle(SEP)events from eruptions such as solar flares and coronal mass ejections(CMEs)can impact Earth and space weather and affect the interplanetary environment through particles(protons and electrons)accelerated to near relativistic(NR)energies,posing a threat to spacecraft,satellites,systems and humans in space.Although the physical mechanisms of the generation,acceleration,and propagation of SEPs are not fully understood,various ongoing studies can uncover characteristics that could contribute to the in-depth analysis of these mechanisms and their potential physical modeling.Therefore,this dissertation firstly studies the NR electron events observed by both ACE and Ulysses.Based on a numerical solution of the Fokker-Planck focused transport equation,we obtained the fluxes of SEPs accelerated is affected by the particle transport conditions in the interplanetary medium and the injection of particles,and establishes the models of SEP peak intensity and peak time of particle injection sources.Subsequently,NR electron events simultaneous observed by ACE,STEREO-A and STEREO-B are studied,and the parameters of the particle source are modeled.Finally,a random particle injection source model is proposed to equivalent random walk of magnetic field lines.In order to study particles acceleration and transport in the heliosphere,it is necessary to use simultaneous observations of SEP time profiles from multiple spacecraft.Studying the 2000 June 10 and 2001 December 26 NR electron events observed by the ACE satellite located at the L1 point and the Ulysses satellite at high latitudes,it can be seen that the time-intensity profiles of NR electrons measured by the two satellites in the same electron event are very different.Through the numerical simulations,we obtain the time-intensity profiles of SEP fluxes,which generally fit well to the observations of the two events.It is found that the reason for the difference in electron flux observed by satellites in the same event is that,in addition to the different positions of the two satellites,the propagation effects of particles(such as perpendicular diffusion effect and adiabatic cooling effect)and the properties of high-energy particle sources also cause differences in the distribution of ACE and Ulysses fluxes.In addition,the differences between different electron events probably caused by the significant difference between the two events,such as those corresponding to flares of different intensities,the relative location of flare and spacecraft,and the solar wind.Moreover,we propose models for the peak intensity of the particle source,the time interval from the flare onset to the particle source peak time,and the half-width of source.The theoretical model fits well with the fitted parameters.Through numerical simulations,we reproduced the time-intensity profiles of five NR electron events observed by the multi-spacecraft ACE,STEREO-A,and STEREO-B near1 AU.The particle injection source model used in the simulations was represented by the Reid-Axford equation,which includes the rise time scale,the decay time scale,the half width of the particle source,and the characteristic peak intensity.By analyzing the statistical relationships between these four particle source parameters and the flare properties,the model of parameters were established.In addition,a model for the magnetic turbulence level was also established.Finally,we evaluated the theoretical models of the particle source parameters and magnetic turbulence level using an additional 12 NR electron events.The results showed that the model was able to predict the peak intensity and fluence of the particles accurately,indicating that the theoretical models constructed could be used for radiation hazard forecasting and estimation.Because of the random walk of interplanetary magnetic lines,the motion of SEPs in the interplanetary magnetic field becomes complicated and the real interplanetary magnetic field is difficult to represent by a certain fixed model.For convenience,the equivalent SEP motion in the random walk of magnetic field lines is constructed to model the random particle injection source.The random injection source model consists of several small injection sources centered on the flare site,and their positions can vary randomly as a function of time.Furthermore,the locations of these small injection sources exhibit a Gaussian distribution.The presented method has been applied to the NR electron events observed by the ACE on 2000 June 10 and 2003 May 31,and the best-fit transport and the electron injection profile parameters are derived.In addition,the time-intensity profiles of NR electron events with special structure,such as the two-peak and curved,can be fitted well by numerical simulations.We also simulate these two electron events using another injection source model with Reid-Axford profile,and this discrepancy between the two simulated time-intensity profiles suggests that the random injection source model performs more efficiently than the other source.