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Interplanetary coronal mass ejections (ICMEs) often consist of a shock wave,sheath region, and ejecta region. The ejecta regions are divided into two broadclasses: magnetic clouds (MC) that exhibit the characteristics of magnetic fluxropes and non-magnetic clouds (NMC) that do not. As CMEs result from eruptionof magnetic flux ropes, it is important to answer why NMCs do not have the fluxrope features. One claims that NMCs lose their original flux rope features dueto the interactions between ICMEs or ICMEs and other large scale structuresduring their transit in the heliosphere. The other attributes this phenomenonto the geometric selection effect, i.e., when an ICME has its nose (flank,including leg and non-leg flanks) pass through the observing spacecraft, the MC(NMC) features will be detected along the spacecraft trajectory within theejecta. In this Letter, we examine which explanation is more reasonable throughthe geometric properties of ICMEs. If the selection effect leads to differentejecta types, MCs should have narrower sheath region compared to NMCs from thestatistical point of view, which is confirmed by our statistics. Besides, wefind that NMCs have the similar size in solar cycles 23 and 24, and NMCs aresmaller than MCs in cycle 23 but larger than MCs in cycle 24. This suggeststhat most NMCs have their leg flank pass through the spacecraft. Our geometricanalyses support that all ICMEs should have a magnetic flux rope structure near1 AU.

Do All Interplanetary Coronal Mass Ejections Have A Magnetic Flux Rope Structure Near 1 AU?