Interpreting density enhancement of coronal mass ejections

Abstract: Coronal mass ejections (CMEs) are some of the extraterrestrialevents most impactful to earth. Eorts to model and predict theireects have seen new possibilities in the two most recent decades dueto multiple new spacecrafts providing a wider range of data than everbefore. Models of these events suer from a number of inaccuracies,one of them being the density ratio between the CME and the ambientsolar wind. Since the arrival time for potentially harmful disturbancespredicted by models has been proved to be highly sensitive to thisparameter we therefore take care to set it as accurately as possible.Traditionally this value is either set to a default, justied by denitionand theory, or set to the density ratio between the bulk if the ejectedgas and the surrounding medium. A proposition has been made tomeasure density enhancement dierently, using a reference point at theshock wave preceding the CME for each event. This method strives toimprove arrival time predictions and was in this paper tested for onecoronal mass ejection event. Two runs if the model WSA-ENLIL+Conewas made; one with the default value of density enhancement, onewith a value determined through the revised method using coronographdata. Running the model with the revised value improved the predictedarrival time by moving it forwards in time by 4h, which was still tooearly. Other input data into the model run was then discussed as apossible cause of the remaining inaccuracy.