Global Energetics of Solar Flares. VII. Aerodynamic Drag in Coronal Mass Ejections

Abstract

The free energy that is dissipated in a magnetic reconnection process of a solar flare, generally accompanied by a coronal mass ejection (CME), has been considered as the ultimate energy source of the global energy budget of solar flares in previous statistical studies. Here we explore the effects of the aerodynamic drag force on CMEs, which supplies additional energy from the slow solar wind to a CME event, besides the magnetic energy supply. For this purpose, we fit the analytical aerodynamic drag model of Cargill and Vršnak et al. to the height-time profiles r(t) of LASCO/SOHO data in 14,316 CME events observed during the first 8 yr (2010-2017) of the Solar Dynamics Observatory era (ensuring EUV coverage with AIA). Our main findings are (1) a mean solar wind speed of w = 472 ± 414 km s^-1, (2) a maximum drag-accelerated CME energy of E _drag ≲ 2 × 10³² erg, (3) a maximum flare-accelerated CME energy of E _flare ≲ 1.5 × 10³³ erg, (4) the ratio of the summed kinetic energies of all flare-accelerated CMEs to the drag-accelerated CMEs amounts to a factor of 4, (5) the inclusion of the drag force slightly lowers the overall energy budget of CME kinetic energies in flares from ≈7% to ≈4%, and (6) the arrival times of CMEs at Earth can be predicted with an accuracy of ≈23%.