HELIOSPHERIC PROPAGATION OF CORONAL MASS EJECTIONS: COMPARISON OF NUMERICAL WSA-ENLIL plus CONE MODEL AND ANALYTICAL DRAG-BASED MODEL

Real-time forecasting of the arrival of coronal mass ejections (CMEs) at Earth, based on remote solar observations, is one of the central issues of space-weather research. In this paper, we compare arrival-time predictions calculated applying the numerical "WSA-ENLIL+Cone model" and the analytical "drag-based model" (DBM). Both models use coronagraphic observations of CMEs as input data, thus providing an early space-weather forecast two to four days before the arrival of the disturbance at the Earth, depending on the CME speed. It is shown that both methods give very similar results if the drag parameter Gamma = 0.1 is used in DBM in combination with a background solar-wind speed of w = 400 km s(-1). For this combination, the mean value of the difference between arrival times calculated by ENLIL and DBM is (Delta) over bar = 0.09 +/- 9.0 hr with an average of the absolute-value differences of vertical bar Delta vertical bar = 7.1 hr. Comparing the observed arrivals (O) with the calculated ones (C) for ENLIL gives O - C = -0.3 +/- 16.9 hr and, analogously, O - C = +1.1 +/- 19.1 hr for DBM. Applying Gamma = 0.2 with w = 450 km s(-1) in DBM, one finds O - C = - 1.7 +/- 18.3 hr, with an average of the absolute-value differences of 14.8 hr, which is similar to that for ENLIL, 14.1 hr. Finally, we demonstrate that the prediction accuracy significantly degrades with increasing solar activity.