Analysis of the substructure within a complex magnetic cloud on 3–4 September 2008

Abstract. In this paper we have analyzed a substructure found within a leading part of a north–south-oriented magnetic cloud (MC) observed on 3–4 September 2008 in the near-Earth solar wind by multiple spacecraft (ACE, Wind, THEMIS B and C). The MC was preceded by a stream interface (SI) and followed by a high-speed stream (HSS). The identified substructure featured a strong depletion of suprathermal halo electrons and showed distinct magnetic field and plasma signatures. It occurred where suprathermal electron flow within a cloud changed from bidirectional to unidirectional, indicating change in the field line connectivity to the Sun. We found that the substructure maintained roughly its integrity from the first Lagrangian point to the vicinity of the Earth's bow shock in the front edge of the MC, but revealed small changes in the structure which could be explained either by temporal evolution or spatial configuration of the spacecraft.