MHD description of the dynamical relationships between a flux rope, streamer, coronal mass ejection, and magnetic cloud: An analysis of the January 1997 Sun-Earth connection event
S. T. Wu, W. P. Guo, D. J. Michels, and L. F. Burlaga
Center for Space Plasma and Aeronomic Research and Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville
We investigate the dynamical relationships between a coronal flux rope, a streamer, a coronal mass ejection (CME), and a magnetic cloud by using observations from the satellites of the International Solar-Terrestrial Physics observatories together with a streamer and flux rope interaction model [Wu and Guo, 1997a]. This is the first physical description of the evolution of a CME related to a flux rope in a streamer near the Sun to a magnetic cloud at 1 AU. The distinctive physical configuration of the model is based on a theoretical suggestion [Low, 1994] and observations [Hundhausen, 1993] that the magnetic structure of a streamer with an embedded cavity provides favorable condition for launch of a CME. We explore this physical scenario by identifying a flux rope as the cavity and using a fully self-consistent numerical simulation to illustrate the dynamical process of evolution of the flux rope/CME into a magnetic cloud. The simulation results are then compared to solar and interplanetary data from the well-observed Sun-Earth connection event of January 6-12, 1997. The data used for this analysis were collected chiefly by the Solar and Heliospheric Observatory (SOHO) Large-Angle and Spectrometric Coronagraph Experiment coronagraph and the solar wind particle and field sensors on the Wind spacecraft, but ground-based solar data were used as well. Because we have detailed observations of the same disturbance both at the Sun (SOHO) and at 1 AU (Wind), this event gives us an unusual opportunity to test the magnetohydrodynamic methodology and to learn about the physical processes of the Sun-Earth connection. In this study we show that when the flux rope rises (owing to increasing axial current, as assumed here, or to some other mechanism), it disrupts the streamer-flux rope system, thus launching a coronal mass ejection. The flux rope then escapes from the streamer and evolves to become a magnetic cloud, as expected, in interplanetary space. The CME is a visible feature moving ahead of the flux rope. The model also predicts a fast-mode shock in front of the magnetic cloud, as observed.
J. Geophys. Res., Vol. 104, No. A7, 14,789-14,801, 1999