Modelling the Sun-to-Earth Propagation of CMEs Using a Novel Flux-Rope Model

One of the major challenges in space weather forecasting is to reliably predict the magnetic structure of interplanetary coronal mass ejections (ICMEs) in the near-Earth space. In the framework of global MHD modelling, several efforts have been made to model the CME magnetic field from Sun to Earth. However, it remains challenging to deduce a flux-rope solution that can reliably model the magnetic structure of a CME. Aiming to improve the space-weather forecasting capability, we implement a new flux-rope model in “European heliospheric forecasting information asset” (EUHFORIA). Our flux-rope model includes an initially force-free toroidal flux-rope that is embedded in the low-coronal magnetic field. The embedding technique adds a significant novelty to the state-of-the-art as it preserves the continuity condition of the magnetic field at the flux-rope boundary and maintains the force-free solution of the flux rope. The dynamics of the flux rope in the low and middle corona are solved by a non-uniform advection constrained by the observed kinematics of the event. This results in a global non-toroidal loop-like magnetic structure that locally manifests as a cylindrical structure. At heliospheric distances, the evolution is modeled as a MHD process using EUHFORIA. We assess our model results on several ICMEs, including cases of interacting events. Comparing the model results with the in-situ magnetic field configuration of the ICME at 1 au, we find that the simulated magnetic field profiles of the flux-rope are in very good agreement with the in-situ observations. Therefore, the framework of toroidal model implementation as developed in this study could prove to be a major step-forward in forecasting the geo-effectiveness of CMEs.