Reconstruction of the 2007 May 22 Magnetic Cloud: How Much Can We Trust the Flux-Rope Geometry of CMEs?

Coronal mass ejections (CMEs) are often assumed to be magnetic flux ropes, but direct proof has been lacking. A key feature, resulting from the translatlonal symmetry of a flux rope, Is that the total transverse pressure as well as the axial magnetic field has the same functional form over the vector potential along any crossing of the flux rope. We test this feature (and hence the flux-rope structure) by reconstructing the 2007 May 22 magnetic cloud (MC) observed at STEREO B, Wind/ACE, and possibly STEREO A with the Grad-Shafranov (GS) method. The model output from reconstruction at STEREO B agrees fairly well with the magnetic field and thermal pressure observed at ACE/Wind; the separation between STEREO B and ACE/WInd is about 0.06 AU, almost half of the MC radial width. For the first time, we reproduce observations at one spacecraft with data from another well-separated spacecraft, which provides compelling evidence for the flux-rope geometry and is of importance for understanding CME initiation and propagation. We also discuss the global configuration of the MC at different spacecraft on the basis of the reconstruction results.