Aerodynamic Drag and Mass of coronal Mass Ejections

Bojan Vrsnak1, Dijana Vrbanec2, Jasa Calogovic1

1Hvar Observatory, Croatia
2Faculty of Science, Department of Physics, Croatia

The dynamics of coronal mass ejections (CMEs) is strongly affected by the interaction of the erupting structure with the ambient magnetoplasma: eruptions that are faster than solar wind transfer the momentum and energy to the wind and generally decelerate, whereas slower ones gain the momentum and accelerate. Such a behavior can be expressed in terms of “aerodynamic” drag.

In our presentation we analyze a statistical dependence of the drag acceleration on the CME mass. We employ a large sample of more than 11000 CMEs observed by the Large Angle and Spectrometric Coronagraph in the radial distance range 2-30 solar radii. A subsample of 3091 events for which CME masses are listed in the LASCO CME Catalog is used to inspect the acceleration-velocity relationship for various classes of CME masses.

It is demonstrated that the slope k of the acceleration-velocity anti-correlation a(v) is smaller for subsamples of larger masses, revealing that massive CMEs are less affected by the aerodynamic drag. The empirically established dependence of the slope k on the CME mass m is very close to the dependence k ~ m-13 which arises from the physical characteristics of the aerodynamic drag. Finally, it is shown that the x-axis intercept v0 of the a(v) regression-line is shifted to larger velocities for subsamples of larger masses, indicating that the driving force is larger in more massive CMEs.

Implications for the space-weather forecasting of CME arrival-times are discussed.