Impacts of a torus model on the geometry of magnetic clouds

K. Marubashi

NICT

We identified 17 magnetic clouds (MCs) with durations longer than 30 hours by surveying 10 years solar wind observations by WIND and ACE spacecrafts. The model fitting analyses were made for these 17 MCs with a torus model, with a special attention paid to the curvature effects expected when the spacecraft traversed the magnetic cloud near the leg of the MC loop. The fitting with a cylinder model was also done when possible. The results indicate that there are 4 different categories in the MC observations: (1) MCs that can be interpreted only with a torus model, because the rotation angles of the magnetic fields are appreciably larger than 180°, (2) MCs that can be interpreted only with a torus model, although the field rotations are smaller than 180°, (3) MCs for which both a cylinder model and a torus model provide acceptable fitting results with similar geometries, and (4) MCs that can be well fitted to both a cylinder model and a torus model, but the resultant geometries are very much different with each other. The existence of the 4th category raises important problems in our understanding of the relationship between the magnetic field structures in MCs and the coronal magnetic field structures.