An interplanetary magnetic cloud (MC) is usually considered the byproduct of a coronal mass ejection (CME). Due to the frequent occurrence of CMEs, multiple magnetic clouds (multi-MCs), in which one MC catches up with another, should be a relatively common phenomenon. A simple flux rope model is used to get the primary magnetic field features of multi-MCs. Results indicate that the magnetic field configuration of multi-MCs mainly depends on the magnetic field characteristics of each member of multi-MCs. It may be entirely different in another situation. Moreover, we fit the data from the Wind spacecraft by using this model. Comparing the model with the observations, we verify the existence of multi-MCs, and propose some suggestions for further work.

Based on the observations of the Sun and the interplanetary medium, a series of solaractivities in late October 2003 and their consequences are studied comprehensively. Thirteen X-rayflares with importance greater than M-class, six frontside halo coronal mass ejections (CMEs) withspan angle larger than 100◦ and three associated eruptions of filament materials are identified byexamining lots of solar observations from October 26 to 29. All these flares were associated with typeIII radio bursts, all the frontside halo CMEs were accompanied by type II or type II-like radio bursts.Particularly, among these activities, two major solar events caused two extraordinary enhancements(exceeding 1000 particles/(cm2 s−1 ster−1 Mev−1) of solar energetic particle (SEP) flux intensity nearthe Earth, two large ejecta with fast shocks preceding, and two great geomagnetic storms with Dstpeak value of −363 and −401 nT, respectively. By using a cross correlation technique and a forcefreecylindrical flux rope model, the October 29 magnetic cloud associated with the largest CME areanalyzed, including its orientation and the sign of its helicity. It is found that the helicity of the cloudis negative, contrary to the regular statistical pattern that negative- and positive-helical interplanetarymagnetic clouds would be expected to come from northern and southern solar hemisphere. Moreover, the relationship between the orientation of magnetic cloud and associated filament is discussed. Inaddition, some discussion concerning multiple-magnetic-cloud structures and SEP events is alsogiven.