Three-dimensional propagation of coronal mass ejections (CMEs) in a structured solar wind flow 1. CME launched within the streamer

A three-dimensional (3-D) numerical hydrodynamic model is used to investigate the temporal and spatial evolution of large-scale solar wind structures. A tilted-dipole outflow configuration is specified at the inner boundary near the Sun, and a structured, corotating solar wind (SW) flow is established by dynamic relaxation. Time-dependent variation of the pressure and velocity at the inner boundary is applied to generate transient structures within the streamer belt. The dynamical interaction of a coronal mass ejection (CME) with the corotating coronal streamer belt flow between 0.14 and 5.04 AU is then investigated. Numerical results show that the motion and appearance of a CME can be strongly affected by its interaction with the velocity and density structure of the background SW. The initial shape and density distribution of the CME is distorted in all dimensions; it is compressed where the CME is trapped between slow streamer belt and high-speed coronal hole flows, and it is distended where the CME penetrates into the trailing edge of the preceding high-speed stream. Thus a given CME can be observed with substantially different properties at different locations; the shock strength as well as the stand-off distance between the shock front and the CME driver gas can vary considerably across the structure, and the density profile through the disturbance can adopt different forms depending on location. Merging of CME and corotating interaction region shocks and thermodynamic structures as demonstrated in this simulation complicate the interpretation of single-spacecraft observations.