The Origin of Magnetic Flux Ropes Observed at 1 AU from the Sun

It is not always easy to know the origin of geomagnetic storms. Interplanetary coronal mass ejections (ICMEs) may be responsible for most of non-recurrent geomagnetic storms. In particular, those containing a flux rope could cause stronger geomagnetic disturbances, depending on the occurrence of enhanced southward magnetic field. We have known examples of such ICMEs that are not clearly connected to low coronal signatures (LCSs). In order to find out how common this phenomenon is, we have isolated in in situ data periods of enhanced magnetic field that is seen to smoothly rotate with time, which can, in the first approximation, indicate the presence of a flux rope. We rank the difficulty of associating these flux rope ICMEs with possible LCSs of the parent CME. When the CME is identified, we more often fail to locate its source region without processing EUV images. Even after image processing, it is sometimes difficult to find the CME source region. To our surprise, some flux rope ICMEs may not be traced back to a CME close to the Sun. We discuss these findings in terms of where and how the eruption starts and evolves into an organized structure, referring to recent simulation results. In some of our examples, another explanation may be possioble for the apparent field rotation found at 1 AU.