Research On The Relationship Between Halo Coronal Mass Ejections And Solar Proton Events

Solar proton event(SPE)is a hazardous event of space weather caused by solar eruptions.It is harmful to space missions and the astronauts,so SPEs gain extra attention in both theoretical researches and daily operational forecast.CME(coronal mass ejection)closely related to SPE,especially the halo CME.We selected all 342 halo CMEs occurring during the period from 1996 to 2015,and 91 of them are corresponding to SPEs.Statistical study found that the SPEs occurrence percentage increases when halo CME speed increases or the latitude of SPEs source is from east to west.The SPEs occurrence percentage exceeds 50% when halo CME speed is more than 1500km/s,and 89% of halo CMEs corresponding to SPEs occurred in the longitude range of E30~W90.In order to better understand the occurrence of SPEs,we took both halo CME speed and source longitude into account simultaneously.Halo CMEs in E30~W90 longitude range with speed greater than 1300km/s have a highest SPEs probability,and these SPEs have larger peak proton flux than others.When we considered the angle distance between the position of halo CMEs source and N0W45,we could get a new understanding.Most halo CMEs corresponding to SPEs have angle distance smaller than 60 degrees.The higher speed is required to produce SPE as angle distance gets larger.In order to obtain a more comprehensive understanding of SPEs and its factors,possible explanations for five typical fast halo CMEs not associated with SPEs are discussed in detail.The results show that deviation of CME direction from the solar ecliptic plane,the low latitude coronal holes near the source of halo CME,the variation of interplanetary magnetic field and turbulence caused by previous activity all are very important to SPEs production.Therefore,daily operational SPE forecast must consider the halo CME explosion characteristics,source region feature and interplanetary environment.