Overview of the WSA–Enlil simulation of the 2021 October 9 CME. (a) Radial slice of the solar wind radial speed at the Enlil inner boundary of 21.5 R_⊙, showing the injection of the CME at its point of maximum width. (b) Same as (a), but for the solar wind number density. (c) View on the ecliptic plane of the solar wind radial speed within the simulation’s heliospheric domain (0.1–2.0 au), showing the CME approaching Earth. (d) Same as (c), but for the normalised solar wind number density. The CME ejecta is traced from its injection based on the density enhancement with respect to the background solar wind (initially set to 4 times the ambient density), and is outlined with a black contour in panels (c) and (d).