Dynamics of CMEs and Evolution of CME Magnetic Fields in Interplanetary Space

Coronal mass ejections (CMEs) constitute an important class of solar wind (SW) structures, having practical implications for geomagnetic conditions. With the new SECCHI/STEREO observations, it is now possible to observe CME trajectories in interplanetary space. This allows direct comparison of CME models with CME data over a much wider region in space than has been possible. Among the existing CME models, the erupting flux rope model (FRM) of Chen (1996) is the best tested model. It has been extensively shown to be able to replicate observed CME dynamics extending to the SECCHI HI1 field of view ( 100 Rs) (Kunkel and Chen 2010). Of the physical CME parameters, the strength and evolution of CME magnetic fields have not been accessible to direct measurement. In a theory-data comparison paper, however, Krall et al. (2006) showed that the FRM solution that best fit the observed halo CME data also yielded a flux rope whose magnetic field at 1 AU was in reasonable agreement with that of a magnetic cloud detected by the ACE spacecraft. This suggests that by fitting observed CME trajectories, the FRM is able to correctly predict magnetic cloud fields at 1 AU. In this talk, I will discuss a systematic study of this possibility. The talk will show in detail how the magnetic field of a CME evolves through interplanetary space, emphasizing the quantitative relationship between the CME trajectory and the evolution of the CME magnetic field. The theory will be applied to CME dynamics observed by SECCHI coronagraphs and the magnetic fields of associated magnetic clouds observed by instruments at 1 AU. The discussion will focus on a physical understanding that can be used to interpret observational data and numerical results of simulation models of CMEs.