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

We investigate the dynamical relationships between a coronal flux rope, a s treamer, a coronal mass ejection (CME), and a magnetic cloud by using obser vations 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 clou d at 1 AU, The distinctive physical configuration of the model is based on a theoretical suggestion [Low, 1994] and observations [Hundhausen, 1993] th at the magnetic structure of a streamer with an embedded cavity provides fa vorable 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 nu merical simulation to illustrate the dynamical process of evolution of the flux rope/CME into a magnetic cloud. The simulation results are then compar ed to solar and interplanetary data from the well-observed Sun-Earth connec tion event of January 6-12, 1997. The data used for this analysis were coll ected chiefly by the Solar and Heliospheric Observatory (SOHO) Large-Angle and Spectrometric Coronagraph Experiment coronagraph and the solar wind par ticle and field sensors on the Wind spacecraft, but ground-based solar data were used as well. Because we have detailed observations of the same distu rbance both at the Sun (SOHO) and at 1 AU (Wind), this event gives us an un usual 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 a ssumed here, or to some other mechanism), it disrupts the streamer-flux rop e system, thus launching a coronal mass ejection. The flux rope then escape s 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 flu x rope. The model also predicts a fast-mode shock in front of the magnetic cloud, as observed.