Cluster observations of the heliospheric current sheet and an associated magnetic flux rope and comparisons with ACE

Abstract

Cluster and ACE magnetic field measurements from the 13 February 2001 are presented. On this day the four Cluster spacecraft made two crossings of the heliospheric current sheet (HCS) while in the solar wind and observed a large‐scale rotation of the magnetic field in the magnetosheath. These features were also observed by ACE upstream of the Earth at the L1 point. Minimum variance analysis (MVA) is used to show the similarity of the HCS orientation at ACE and Cluster, and Cluster multispacecraft analysis of the timing, orientation, and changes across the reversal is used to show that these results are consistent with crossings of the HCS. The structure of the currents in the HCS is also investigated using the Cluster curlometer technique. The field rotation observed by Cluster in the magnetosheath and ACE in the solar wind is identified as a magnetic flux rope, and MVA shows that although the structure and ordering of the flux rope are unchanged by the bow shock, the orientation of the axis changes. This is most likely caused by the rotation of the interplanetary magnetic field (IMF) as it is processed by the bow shock, augmented by draping effects deeper in the magnetosheath.