Discussion on the Identification of Magnetic Cloud Boundaries Using Cloud Natural Coordinate System

Magnetic clouds (MCs) belong to an important subset of interplanetary coronal mass ejections. The identification of their boundaries is always a problem in the studies of MCs. This paper discusses a method to identify the boundaries of MCs by coordinate transformation. Instead of the conventional GSE (Geocentric Solar Ecliptic) coordinate system, the interplanetary magnetic field data are converted into a cloud natural coordinate system, in which the profile of the MC as a magnetic flux tube is clearly displayed. Then, combining with the plasma properties of the MC, the boundary of the cloud can be identified easily. Six observed MCs are analyzed using this method, and the results show that this method is feasible and can reduce the uncertainty in the identification of MC boundaries.