A numerical study of the Drag parameter for the description of ICME dynamics

Coronal Mass Ejections are violent phenomena of solar activity with repercussions throughout the entire heliosphere. They are the major cause of geomagnetic disturbances, with severe risks for space missions and Earth economy. Nowadays, the prediction of the arrival of such events at Earth one of the primary tasks in Space-Weather forecasting. This can be made through use of numerical model to simulate the state of the solar wind, or simplified models, based on experimental laws and a reasonable choice of features, which are largely employed to provide quick forecasts. One of these models is the “Drag-Based Model”, stating that the dynamics of a CME is mainly governed by its interaction with the solar wind. This model requires two parameters to run a forecast: the solar wind speed and the drag parameter, which quantifies the interaction between the moving CME and the ambient solar wind. Little is known about these parameters and their evaluation is based on statistics collected from past records. In this work we perform numerical simulation of solid bodies moving in an external fluid, representative of CMEs moving into the solar wind, to compute the drag force they experience. Results are then compared with typical values of the drag parameters employed in the Drag-Based model, and possible refinements, for the purpose of improving forecast accuracy through the DBM, are discussed.