Determining DBM initial parameters (Vsw and γ) for CME forecasting

Determine the initial Drag-Based Model parameters—the background solar wind speed Vsw and the drag parameter γ—for specific coronal mass ejection events so that the model can be initialized in a physically consistent and event-appropriate manner for forecasting CME arrival time and speed at Earth.

Background

The drag-based model (DBM) represents CME propagation through an analytical formulation where the acceleration depends on the difference between the CME speed and the ambient solar wind speed, scaled by a drag parameter γ. Standard DBM practice assumes constant values for Vsw and γ, but the authors emphasize that properly determining these initial parameters is a persistent difficulty.

In this study, the authors use nominal mean values for Vsw and γ and explore their impact via ensembles, demonstrating substantial sensitivity of predicted CME arrival time and speed to these parameters. This sensitivity underscores the need for reliable methods to estimate Vsw and γ for each event, motivating the explicit identification of their determination as an open issue.