Research On The Longitudinal Properties Of SEP Events Based On Multi-Point Observation

The study of solar energetic particle(SEP)events has always been one of the key research objects of space weather,which will have a serious impact on aerospace,national defense,military,civil life and economy.The relative longitude between the magnetic foot of the observation satellite and the source region of SEP has a great influence on the effective observation of SEP,that is,the observation of SEP events has a strong longitude dependence.The study of the longitude distribution of the observed characteristics of SEP events is of great significance for understanding the relationship between SEP events,coronal mass ejections(CMEs)and flares,as well as space weather modeling and forecasting of SEP events.In this thesis,to study the characteristics of meridional distribution for SEP events,joint based on satellite observations,screening of the solar cycle 24 December 2006 to October2017,during the 122 solar energetic particle events and their coronal mass ejections,analyzed the SEP event attributes along with the change of relative longitude and SEP and longitude distribution of the correlation between CME attributes,and its associated with SEP events Fe/O ratio,which can represent seed population,velocity and using the velocity analysis method for the SEP events flux profile change causes and mechanism research.The results are shown as follow:(1)The characteristic parameters of SEP events have obvious longitude distribution law.The SEP characteristic time T_O(burst time to half peak time)and T_R(half peak to peak time)increase with the relative longitude,while Du(duration)and I_p(peak flux)decrease with the relative longitude.In addition,the correlation between characteristic parameters of SEP events and accompanying CME attributes changes significantly with relative longitude:In the position with good magnetic connection(such as the relative longitude[-30°,30°]),T_O is negatively correlated with CME velocity,mass,kinetic energy and other attributes,while T_Ris positively correlated with them,while there is no significant correlation at other positions.Compared with other locations,Du and I_p have stronger correlation with CME velocity in the region with better magnetic connection(0.60 and 0.75),and the correlation coefficient decreases significantly with the increase of relative longitude(lower than 0.46 and 0.56).(2)The characteristic attributes and dependence on longitude of SEP events with different element abundances(distinguished by Fe/O ratio)are obviously different.The peak flux of low Fe/O SEP events is usually higher than that of high Fe/O events,and large SEP events generally have a low Fe/O ratio.Compared with low Fe/O events,high Fe/O events are accompanied by smaller CMEs in terms of velocity,mass and kinetic energy,but they have a faster flux rise rate.The duration Du and peak flux I_p of SEP are positively correlated with CME velocity,and the correlation between I_p and Du of SEP events of low Fe/O events and CME is higher than that of events of high Fe/O events.(3)The secondary enhancement of the flux profile of the gradual SEP event is caused by many factors,including solar flare,CME shock,type?radio burst and its enhancement,interplanetary disturbance,etc.According to the variation law of the SEP flux in each energy channel,the enhancement of the influence near the sun shows obvious velocity dispersion,while the influence of the local interplanetary disturbance shows simultaneous enhancement or weakening of the flux in multiple energy channels without obvious velocity dispersion.In addition,no significant SEP flux enhancement was observed at the beginning of type II radio burst enhancement.In conclusion,the observation attributes of SEP events are affected by both CME attributes(such as velocity,kinetic energy,etc.)and the relative longitude between the observation point and the source.The better the magnetic connection is,the greater the intensity of the observed SEP events is,and the higher the probability of observing large SEP events is,and the better the correlation between the observed characteristics and CME attributes is,and the stronger the influence of CME is,which has very important practical significance for space weather forecast of large SEP events.At the same time,the weakening of the correlation between high Fe/O SEP events and CME suggests that the factors such as flare acceleration and seed population also play an important role in the generation of these SEP events.In addition,the study on the secondary enhancement of the flux profile of SEP events can help us better understand the acceleration process of SEP and the influencing factors of flux variation.