Statistical Study On Interplanetary Coronal Mass Ejections During1996-2012near1AU

As one of the major interplanetary origins of disastrous space weather of earth,interplanetary coronal mass ejections (ICMEs) have many signatures which aredifferent from general solar wind. On the basis of associated satellite data and theexisted ICME list, we have made statistical analysis on ICMEs and their sheathsduring the whole solar cycle23. We also made comparative studies between ICMEsduring the first four years of solar cycles23and those during the first four years ofsolar cycle24.ICMEs can be divided into two categories including magnetic cloud ICMEs(MC-ICMEs) and non-cloud-like ICMEs (non-MC-ICMEs), based on the signaturesof the magnetic field. We also made comparative studies between magnetic cloudstructures and general ICMEs. During the entire solar cycle23, there are317ICMEs,of which33.75%are MC-ICMEs and the other66.25%are non-MC-ICMEs. We findthat the yearly variation of non-MC-ICMEs is well correlated with the variation ofsunspots while this correlated relationship between variations of MC-ICMEs andsunspots is not fulfilled. On the contrary, the MCs-to-ICMEs ratio shows anapproximately anticorrelated relation.Comparative study on parameters of MC-ICMEs and non-MC-ICMEs as well asMCs and general ICMEs shows that the magnetic field strength, the plasma densityand the proton temperature of MC-ICMEs and MCs surpass those of non-MC-ICMEsand general ICMEs respectively, which means that magnetic clouds are specialICMEs with more intense magnetic field strength, larger plasma density and higherproton temperature. And both the temporal scale and the spatial scale of MCs exceedthose of non-MC-ICMEs.Comparative studies between parameters of MC-ICME sheaths and those ofnon-MC-ICME sheaths during the whole solar cycle23show almost the same resultsas those of MC-ICMEs and non-MC-ICMEs. MC-ICME sheaths have strongermagnetic field strength, larger plasma density, higher proton temperature and slowertransiting speed than non-MC-ICME sheaths. But both of them have almost equal spatial scales.Based on the analysis of geomagnetic response to MC-ICMEs as well as theirsheaths and to non-MC-ICMEs as well as their sheaths during the whole solar cycle23, we find that the former is more intense than the latter. The special structure(smoothly rotated magnetic field with large angle) and stronger southward magneticfield of MCs with respect to general ICMEs should be responsible for the result.We also make a comparative study on the properties of ICMEs in the first fouryears of solar cycles23and24, which have very different solar activities. Accordingto the analysis, there are97and89ICMEs during the first four years of solar cycles23and24, respectively. The ICME parameters including magnetic field strength,solar wind speed, plasma density, proton temperature, temporal scale and spatial scalein the first four years of solar cycle23exceed those of solar cycle24obviously. Themean values of the parameters of ICMEs in the rising phase of solar cycle23surpassalmost all of those in solar cycle24year by year.The statistical study of theD stindex shows that the geomagnetic stormstriggered by ICMEs and their sheaths in the rising phase of solar cycle23are muchmore intense than those of solar cycle24. The direct cause should be related to thedifferent magnetic field strengths, southward magnetic field strengths, transitingspeeds andE y, while the root reason may be the extremely low solar activityintensity during the rising phase of solar cycle24.