### Aerodynamic Drag and Mass of coronal Mass
Ejections

**Bojan Vrsnak**^{1},
Dijana Vrbanec^{2}, Jasa Calogovic^{1}

^{1}Hvar Observatory,
Croatia

^{2}Faculty 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^{-1∕3}
which arises from the physical characteristics of the aerodynamic drag. Finally,
it is shown that the x-axis intercept v_{0}
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.