On The Relationship Between SEP Events And CME Eruptions By The Observations Of Multi-vantage Spacecraft

The relationship between Solar Energetic Particle(SEP)events and Coronal Mass Ejection(CME)plays an important role in space weather.Although all gradual SEP events are associated with the fast CME,there are also a lot of large CMEs that do not produce SEP events.As a continuing research of twin-CME scenario,our statistical analyses are on the fast CMEs from Jan.2007 to Sept.2014、interacting CME pairs from Jan.2010 to Aug.2014.The main results are as follows:(1)The threshold of defining a large SEP event(measured by GOES spacecraft is>10MeV flux ＞ 10pfu)is to be larger than 0.01 and 0.014[cm2 · s· sr · MeV-1]respectively for SOHO/EPHIN 25-53 MeV channel and STEREO/HET 23.8-60 MeV channel.(2)The multiple-point observations can well remove the false twin-CME events caused by the projection effect.Our results show that the percentage of misidentification of twin-CMEs by only one spacecraft(e.g.SOHO)is generally lower than 10%,and not more than 15%ultimately.The correlation between SEP peak intensity and CME speed,kinetic energy in single-CME events is significantly higher than that in twin-CME events.The results that inferred from three-view observations are similar to that of single-view.There may be many preceding CMEs for one main CME.Despite of some false identification of twin-CMEs using only single-view observations,it seems not to effect on the statistical results distinctly.(3)We found that all large SEP events were associated with the interacting CMEs accompanying with enhanced type II radio bursts,which also have wider longitudinal distributions comparing to the non-radio-enhanced events(small SEP events).It seems that the type Ⅱ radio bursts enhancement is a good discriminator between large SEP and small or none SEP event producers during CME interactions.We suggest that a fast CME with enough energy completely overtaking its relative narrow preceding CME,especially in low height,can drive more energetic shock signified by type II radio burst enhancement,and the shock can accelerate particles(likely provided by the preceding CME)efficiently and lead to large SEP events.It’s easily interpreted that,when the fast and wide CME completely sweeps up the narrow and slow preceding CME,the particle acceleration of the shock becomes more efficiently either because of the enhanced seed particles injected into the shock surface or because of the trapping and acceleration repeatedly of the energetic particles in the closed flux loop of pre-CMEs intersecting with the shock surface.In summary,we found that there is a strong correlation between large SEP events and twin-CME or interacting CME,and the results of multi-vantage spacecraft are same as that of single spacecraft.The error rate of single satellite identifying twin-CME is given in this paper(generally<10%),which can provide the reliability for the statistical study of the relationship between the multiple CME and the SEP events.However,for the detailed operating mechanism of acceleration,it is still necessary to further study,such as whether preceding CME first provides seed particles or provides closed loops connecting to the shock surface,and a few CMEs do not interact with other CMEs,but also produce SEP events.