Multi-spacecraft study with the Icarus model

Context. Coronal mass ejections (CMEs) are the main drivers of the disturbances in interplanetary space. Earth-directed CMEs can be dangerous, and understanding the CME interior magnetic structure is crucial for advancing space weather studies. It is important to assess the capabilities of a numerical heliospheric model, as a firm understanding of the nature and extent of its limitations can be used to improve the model and the space weather predictions based on it. Aims. The aim of the present study is to test the capabilities of the recently developed heliospheric model Icarus and the linear force-free spheromak model that has been implemented in it. Methods. To validate the Icarus space weather modelling tool, two CME events were selected that were observed by two spacecraft located near Mercury and Earth, respectively. This enables us to test the heliospheric model computed with Icarus at two distant locations. The source regions for the CMEs were identified, and the CME parameters were determined and later optimised. Different adaptive mesh refinement levels were applied in the simulations to assess its performance by comparing the simulation results to in situ measurements. Results. The first CME event erupted at 15:25 on July 9, 2013. The modelled time series were in good agreement with the observations both at MESSENGER and ACE. The second CME event started at 10:25 on February 16, 2014, and was more complicated, as three CME interactions occurred in this event. It was impossible to recover the observed profiles without modelling the other two CMEs that were observed, one before the main CME and one afterward. The parameters for the three CMEs were identified and the three CMEs were modelled in Icarus. For both CME studies, AMR level 3 was sufficient to reconstruct small-scale features near Mercury, while at Earth, AMR level 4 was necessary due to the radially stretched grid that was used. Conclusions. The profiles obtained at both spacecraft resemble the in situ measurements well. The current limitations of the space weather modelling tool result in an excessively small deceleration of the CME propagation during the CME-CME interaction as measured by MESSENGER and ACE.