Interpreting density enhancement of coronal mass ejections

Abstract

Coronal mass ejections (CMEs) are some of the extraterrestrial events most impactful to Earth. Efforts to model and predict their ejects have seen new possibilities in the two most recent decades due to multiple new spacecrafts providing a wider range of data than ever before. Models of these events suffer from insufficient knowledge about their input parameters. One example is the density ratio between the CME and the ambient solar wind. Since the arrival time for potentially harmful disturbances predicted by models has been proved to be highly sensitive to this parameter we therefore take care to set it as accurately as possible. Traditionally this value is either set to a default value or set to the density ratio between the bulk of the ejected gas and the surrounding medium. In this study, we estimate this density enhancement directly from coronagraph data, using a reference point at the shock wave preceding the CME for each event. This method strives to improve arrival time predictions and was in this study tested for one coronal mass ejection event. Two runs of the model WSA-ENLIL+Cone was made; one with the default value of density enhancement, one with a value determined through the revised method using coronograph data. Running the model with the revised value improved the predicted arrival time by moving it forwards in time by 4h, which was still too early. Other input data into the model run are discussed as possible causes of the remaining inaccuracy.

Results

Stereo-A image with the line used for estimating the density from the light intensity indicated.