Observational evidence for velocity convergence toward magnetic neutral lines as a factor in CME initiation

Abstract

One of the major challenges of space weather research and modeling is the identification of the mechanism(s) for coronal mass ejections (CMEs). A leading candidate tested in several recent numerical simulations is photospheric magnetic flux cancellation by velocity convergence toward the neutral line of an active region having sheared or twisted magnetic fields. These attributes have been assumed in various combinations in modeling studies, but little observational work has been done that demonstrates their presence. In this paper, we show observational evidence that this process is at work in two different types of repetitively eruptive active regions in late 1996 and early 1997. The horizontal velocity field is obtained by applying Local Correlation Tracking (LCT) technique to sequences of photospheric line-of-sight magnetograms.