Modeling of Flux Rope Coronal Mass Ejections

Abstract

We present a forward-modeling technique for flux rope-like CMEs using an empirically defined model of a flux rope, the graduated cylindrical shell (GCS). To compare it with white-light coronagraph observations, we assume an electron distribution through the GCS and derive synthetic images in total and polarized brightness for various projections of the model using a Thomson scattering ray-tracing program. We test our forward modeling technique on 34 LASCO CMEs analyzed by Cremades & Bothmer. We are able to reproduce the CME morphology and derive the electron density (at the CME front) of these events using multi-instrument observations (MDI, Hα, EIT, LASCO) under the assumption of self-similar expansion. This study suggests that a flux rope-like structure is a good description for these events. We also find that we need to invoke a deflection and/or rotation of the structure relative to the position and orientation of the source region in most cases. Finally, we demonstrate an original technique to fit the electron density of the CME leading edge. We find that, on average, the peak of the density at the CME front is 7.5 times that in the equatorial model of Saito et al., and can reach ~22 times the model in some cases.