Study Of Propagation Of Solar Energetic Particles Accelerated By The Coronal Mass Ejection Driven Shock

The propagation process of solar energy particle(SEP)in the interplanetary space is a significant subject of the space physics research.The shock driven by coro-nal mass ejection(CME)is a typical kind of solar energy particle source.The study of the SEP propagation accelerated by the CME driven shock with the multi-satellite observation makes so much sense on the understanding of the SEP characteristics.In this paper,further research is taken on the three-dimensional focus transport model of SEP,with which the Shock Particle Transport Code(SPTC)is developed.Through the analysis of the single typical SEP events and multiple events statisti-cally with common characteristics of SEP,we study the SEP transport considering the CME driven shock as a moving particle source in the 3-D Parker magnetic field.With the comparison of simulation results and observations analysis,we focus on the issue of the SEP flux,timescales and peak intensity observed with several different observation locations in the interplanetary space,and analyze the internal physical mechanism behind the observation.The main research contents are as follows.For the traditional single typical SEP events,we choose the 2012 July 23 SEP event to simulation.An extremely powerful,superfast interplanetary coronal mass ejection(ICME)burst from the Sun on 2012 July 23,which was detected by multiple spacecrafts like STEREO and ACE.We use the Parker’s spiral magnetic field model to analysis qualitatively the relationship between the propagation of the CME driven shock in the interplanetary and the associated SEP flux observed by the multi-spacecraft.Then We simulate the event based on the observation data,by solving the SEP transport equation considering ICME shocks as energetic particle sources.The good contrast between simulations and observations offer us the physical mechanisms behind the observations.For the multiple SEP events with common characteristics,we choose a research based on the observation data analysis by S.W.Kahler to simulate and compare.Recently,S.W.Kahler studied the timescales of SEP events associated with CMEs from analysis of spacecraft data.They obtained different timescales for SEP events,such as TO,the onset time from CME launch to SEP onset,TR,the rise time from onset to half the peak intensity(0.5I_p),and TD,the duration of the SEP intensity above 0.5I_p.In this work,we solve the transport equation for SEPs considering ICME shocks as energetic particle sources.With our modeling assumptions,our simulations show similar results to Kahler’s analysis of spacecraft data,that the weighted average of TD increases with both CME speed and width.Moreover,from our simulation results,we suggest TD is directly dependent on CME speed,but not dependent on CME width,which were not found in the analysis of observational data.We study the onset time of SEP flux with two different methods.The one is a simulation method,which suggested the onset time is when a first particle is detected by the observer.The other one is the observation background method,which proposed the onset time is determined by the inflection point between the background and the rise on the SEP flux time profile.The SEP timescales TO and TR defined by S.W.Kahler shown in the last paragraph are associated with the SEP onset time.In this work,we solve the transport equation for SEPs considering ICME shocks as energetic particle sources.We obtain the SEP timescales TR,TO with the two method by simulating the SEP transport.The simulation results which are consistent with the observation,suggested that TR increase with the increasing CME speed and width,and TO is not presented a good regularity with complexed factors.Moreover,when the source location longitude is far away from the observer,as so many factors affecting timescales TR and TO,the different SEP onset time method has little effect on the results.When the source location is close to the observer,the simulation results with the observation background method is more consistent with the observation conclusion.For the multiple SEP events with common characteristics,we summarize a sta-tistical simulation method proposed in the previous work.The observation events are classified and sorted according to several indicators,and with the method of picking out the median value of each group as the typical value,hundreds of events are refined into several characteristic events to simulation.Thus,the numerical simulation time is simplified,and single variable can be controlled and its influence on the researched quantity can be investigated.We used this method to study the correlation between SEP peak intensity with the CME speed and the longitude po-sition,and the corresponding conclusions were obtained by comparing observational data analysis.This method makes up for the defects that the effect of a single factor on the event is always incapable by the observation analysis.It also simplifies the numerical simulations number of the multiple individual events.The method is a good combination of numerical simulation and observation analysis.