Dynamics of coronal mass ejections. The mass-scaling of the aerodynamic drag

Abstract

Context: Coronal and interplanetary propagation of coronal mass ejections (CMEs) is strongly affected by aerodynamic drag.
Aims: The dependence of the drag acceleration on the mass of the CMEs is investigated to establish a quantitative empirical relationship, which might be important in semi-empirical space-weather forecasting.
Methods: We employ a large sample of CMEs observed in the radial distance range of 2-30 solar radii by the Large Angle and Spectrometric Coronagraph on board the SoHO mission to statistically analyze the acceleration-velocity relationship in subsamples of various classes of CME masses.
Results: It is demonstrated that the slope and the v-axis intercept of the anti-correlation of the CME acceleration a and velocity v depend on the mean mass of CMEs included in the sample. The slope k of the correlation is less steep for subsamples of higher masses, revealing that massive CMEs are less affected by the aerodynamic drag. Furthermore, it is found that the v-axis intercept is shifted to higher velocities for subsamples of higher masses. This indicates that, on average, the driving force is greater in more massive CMEs.
Conclusions: The empirically established dependence of the a(v) slope on the CME mass is very close to the dependence kpropto m^-1/3 which follows from the physical characteristics of the aerodynamic drag.