Dynamics of coronal mass ejections

The mass-scaling of the aerodynamic drag

Hvar Observatory, Faculty of Geodesy, Kačićeva 26, 10000 Zagreb, Croatia e-mail: bvrsnak@geof.hr

Received: 18 May 2008
Accepted: 30 July 2008

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 slope on the CME mass is very close to the dependence which follows from the physical characteristics of the aerodynamic drag.