Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections - Liu,YD; Luhmann,JG; Kajdic,P; Kilpua,EKJ; Lugaz,N; Nitta,NV; Moestl,C; Lavraud,B; Bale,SD; Farrugia,CJ; Galvin,AB (NATURE COMMUNICATIONS, 2014)