Modelling the propagation of coronal mass ejections with COCONUT: implementation of the Regularized Biot-Savart Laws flux rope model

Abstract: Context: Coronal mass ejections (CMEs) are rapid eruptions of magnetized plasma that occur on the Sun, which are known as the main drivers of adverse space weather. Accurately tracking their evolution in the heliosphere in numerical models is of utmost importance for space weather forecasting. Aims: The main objective of this paper is to implement the Regularized Biot-Savart Laws (RBSL) method in a new global corona model COCONUT. This approach has the capability to construct the magnetic flux rope with an axis of arbitrary shape. Methods: We present the implementation process of the RBSL flux rope model in COCONUT, which is superposed onto a realistic solar wind reconstructed from the observed magnetogram around the minimum of solar activity. Based on this, we simulate the propagation of an S-shaped flux rope from the solar surface to a distance of 25 solar radii. Results: Our simulation successfully reproduces the birth process of a CME originating from a sigmoid in a self-consistent way. The model effectively captures various physical processes and retrieves the prominent features of the CMEs in observations. In addition, the simulation results indicate that the magnetic topology of the CME flux rope at around 20 solar radii deviates from a coherent structure, and manifests as a mix of open and closed field lines with diverse footpoints. Conclusions: This work demonstrates the potential of the RBSL flux rope model in reproducing CME events that are more consistent with observations. Moreover, our findings strongly suggest that magnetic reconnection during the CME propagation plays a critical role in destroying the coherent characteristic of a CME flux rope.