Inferring of flux rope orientation with the minimum variance analysis technique

Abstract

The accuracy in flux rope orientation inference from both the traditional magnetic‐field‐based minimum variance analysis (BMVA) technique and the current‐based MVA (CMVA) approach is examined. Four different flux rope models are used in the MVA test. It is found that the directions of eigenvectors of MVA are critically dependent on the spacecraft path relative to the flux rope axis and structure of the flux rope encountered. For force‐free flux ropes, the M direction of BMVA best fits the axial orientation, while for non‐force‐free flux ropes the BMVA may fail as the orientation inference tool. Magnetic field data from a single satellite path through non‐force‐free flux ropes are often insufficient to determine the rope orientation. Uncertainty may appear, as neither the N nor the M eigenvector is close to the axial direction. On the other hand, the CMVA based on multiple spacecraft measurements may help to eliminate such an uncertainty and shows great effectiveness for study of structures and geometries of the observed flux ropes.