Geometry of the 20 November 2003 magnetic cloud

摘要

This study is an attempt to find a coherent interpretation of the link between the 20 November 2003 magnetic cloud (MC) and its solar source. Most previous studies agree on the orientation of the MC, but the orientation is nearly perpendicular to the axis of the post-eruption arcade (PEA) or the orientation of the neutral line in the solar source region. We first determine the geometry of this MC by fitting methods with both torus and cylinder models. Three possible geometries are obtained, which can reproduce the observed magnetic field variations associated with the MC, one from the cylinder fit and two from the torus fit. The cylinder fit gives the MC orientation with a tilt of a large angle (～60° ) from the ecliptic plane and nearly perpendicular to the PEA axis, being similar to those from previous studies. In contrast, two torus fit results give the MC axis with tilt angles less than 20° from the ecliptic plane. The two torus results correspond to the spacecraft encounter with the eastern flank of the flux rope loop (model A) and the western flank of the loop (model B), respectively. In either case, the orientation of the loop around the apex is nearly parallel to the PEA as observed by the SOHO/extreme ultraviolet imaging telescope instrument in the most plausible solar source region of a halo coronal mass ejection (CME), which appeared in the field of view of Large Angle and Spectrometric Coronagraph (LASCO) C2 at 08:50 UT, 18 November 2003. The magnetic helicity of the PEA region is positive in agreement with the helicity of the MC. The 3-D reconstruction from the Solar Mass Ejection Imager data shows that the main part of the ejected plasma expands mainly to the west of the Sun-Earth line. Thus, we reach the most straightforward interpretation of the link between the MC and its solar source as follows. The MC was created in association with the launch of the CME that was first observed by the LASCO C2 at 08:50 UT, 18 November 2003, and propagated through interplanetary space with its orientation almost unchanged. The spacecraft encountered the eastern flank of the loop as described by model A.