Multiple magnetic clouds in interplanetary space: A review and perspective

Multiple magnetic clouds are a particular complex structure in interplanetary space. They are formed due to the chase and interaction between successive coronal mass ejections (CME), and thought to be significantly geoeffective. The multiple-magnetic-cloud structure was first reported in 2002, and lots of relevant research has been carried out since. This paper gives a brief review of research on multiple magnetic clouds, in which the following issues are addressed. ① What is the magnetic cloud? ② What is the multiple-magnetic-cloud structure? ③ Why do we study the multiple-magnetic-cloud structure? ④ What is the challenge?