Effects Of Large-scale Coronal Magnetic Field Configuration On The Acceleration And Release Of Solar Energetic Particles

During solar eruptions such as flares and coronal mass ejections,a large number of particles can be accelerated to high energy,called Solar Energetic Particle events,which can result in sighificant enhancement of energetic particle flux in near-Earth space.Ground level enhancement(GLE)events are a category of extremely intense SEP events,mainly accelerated by CME-driven shocks near the Sun.These high-energy particles can cause violent disturbances in the Earth’s magnetosphere and ionosphere,disrupting satellite navigation and communications.The acceleration and release of energetic particles is an outstanding question in solar physics.In this work,we analyze two GLE events in solar cycle 24,to study the effects of large-scale magnetic field configuration on particle acceleration and release.In chapter 2,we present the satellite data and models utilized in this paper.The data is mainly sourced from in-situ observations and remote sensing imaging of various satellites including GOES,STEREO,SOHO,among others.We reconstruct the threedimensional structure of the shock wave,utilizing the ellipsoid shock wave model,and combine it with the observations and imaging of SOHO and STEREO-A.We calculate the position and velocity information of the shock from the obtained fitting parameters.The PFSS model can reproduce the large-scale magnetic field structure of the coronal magnetic field.We combine this with the shock reconstruction results to analyze the interaction between the initial shock and the coronal magnetic field.Additionally,we trace the magnetic field lines near the Earth back to the source surface and the photosphere,and study the magnetic connection between the shock and the satellite near the Earth.In chapter 3,we conduct a comparative analysis of the two GLE events on 2012 May 17(GLE 71)and 2017 September 10(GLE 72),respectively.Temporal variations of the SEP intensity profiles and energy spectra display different patterns in the two events.In GLE71 event,The particle intensity of the event quickly peaked and then dropped slowly,with the energy spectra quickly evolve into a power-law.In GLE72 event,the particle intensity had a longer rising phase,and remained at this level for an extended period after reaching the peak.The spectra indicates that the event hardens at first and then gradually softens.These observations were made by combining whitelight and extreme ultraviolet imaging,we study the interaction of CMEs with coronal streamers in two events.In GLE71 event,the CME originates from the bottom of the streamer belt,while in GLE72 event,the CME originates from the edge of the streamer belt,which makes the initial shock geometry of the two events very different.The magnetic connection between the observer and the shock also affects the locally detected particle intensity and onset time.According to the result of potential field source surface extrapolation,we have traced the magnetic field lines near the Earth back to the surface of the Sun.We found that in the GLE71 event,the magnetic field lines near the Earth were connected to the active region in the early stage of the eruption.According to the results of shock wave reconstruction,the outermost shock front reached 2.4 R⊙ when the GeV particles are released.At this time,the magnetic field lines near the Earth are connected to the shock nose,and the shock front sweeps the corona streamer cusp.In the GLE72 event,the magnetic field lines near the Earth were not connected to the shock at the beginning of the eruption,and the corresponding shock height was 3.7 R⊙ when the GeV particles were released.The results show that the reason for the difference in particle release heights and the locally observed evolution differences between the two events,due to the effect of the large-scale coronal magnetic field configuration on particle acceleration and release.This work draws the following conclusions:the highest-energy particles are primarily accelerated in the shock-streamer interaction regions,i.e.,at the nose of the shock in GLE 71 and the eastern flank of the shock in GLE 72,due to quasi-perpendicular shock geometry and confinement of closed field lines.Subsequently,they are released to the field lines connecting to thenear-Earth spacecraft when the shocks move through the cusp of the streamers.This paper analyzes the acceleration and release source region of the highest energy particles in the GLE event,and reveals the effect of the coronal magnetic field configuration on the particle acceleration,which is in good agreement with previous simulation work.Finally,we present our future research plans and prospects.