HR: 0800h
AN: SH11A-0257    [Abstracts]
TI: Analysis of Magnetic Clouds Based on a Torus-shaped Flux Rope Model
AU: * Marubashi, K
EM: k.marubashi@eos.ocn.ne.jp
AF: CSS, 660-73 Mizuno, Sayama, Saitama, 350-1317 Japan
AU: Lepping, R P
EM: Ronald.P.Lepping@nasa.gov
AF: NASA-Goddard Space Flight Center, Greenbelt, Greenbelt, MD 20771 United States
AB: A magnetic flux rope model is widely accepted as the internal magnetic field structure of magnetic clouds. The global configuration of magnetic clouds is proposed to be a loop-shaped structure extending from the Sun with both ends rooted on the Sun, and deformed to match the Parker spiral. If magnetic clouds really have such configuration, a cylindrical flux rope model can explain the observed magnetic field variations when the spacecraft traversed the central part of the loop. When the spacecraft traversed the curved portions of the loop, however, curvature effects must be taken into consideration to explain the observed field variations. The curvature effects can be taken into account by using a torus-shaped flux rope model. Many studies of magnetic clouds have been made with cylinder models but only much fewer studies were done with torus models. Judging from the proposed global configuration of magnetic clouds, there should be more encounters with magnetic clouds at the curved portions. This is an attempt to find out as many magnetic cloud events as possible that can be well fitted to the torus model. For this purpose, using the solar wind data from ACE, we selected those magnetic cloud events which exhibit smooth rotations of magnetic fields with durations longer than 30 hours. Then, we performed the model fitting analyses for those selected events with both cylinder and torus models, when possible. The results are: (1) For magnetic clouds with field rotations larger the 180 degrees, only fitting with a torus model gives a reasonable result; (2) For those magnetic clouds which could be fitted to both cylinder and torus models, better results are generally obtained by a torus model. It is important to point out here that the two models yield very different geometrical parameters such as width and orientation. The fitting analysis does not necessarily give the real configuration of magnetic clouds. However, we shall be able to judge which one is the most appropriate results by comparing the flux rope axis direction with discontinuities near the magnetic cloud surface. Geometrical relationships between the magnetic clouds and coronal magnetic structures can provide another key to the judgment for determining the real magnetic cloud structure. We point out a possibility that some of the magnetic clouds which were explained by a straight cylinder can be curved structures in reality.
DE: 9800 GENERAL OR MISCELLANEOUS
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005