Numerical simulations of fast and slow coronal mass ejections - AstrophysicsReport as inadecuate

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Abstract: Solar coronal mass ejections (CMEs) show a large variety in their kinematicproperties. CMEs originating in active regions and accompanied by strong flaresare usually faster and accelerated more impulsively than CMEs associated withfilament eruptions outside active regions and weak flares. It has been proposedmore than two decades ago that there are two separate types of CMEs, fast(impulsive) CMEs and slow (gradual) CMEs. However, this concept may not bevalid, since the large data sets acquired in recent years do not show twodistinct peaks in the CME velocity distribution and reveal that both fast andslow CMEs can be accompanied by both weak and strong flares. We presentnumerical simulations which confirm our earlier analytical result that aflux-rope CME model permits describing fast and slow CMEs in a unified manner.We consider a force-free coronal magnetic flux rope embedded in the potentialfield of model bipolar and quadrupolar active regions. The eruption is drivenby the torus instability which occurs if the field overlying the flux ropedecreases sufficiently rapidly with height. The acceleration profile depends onthe steepness of this field decrease, corresponding to fast CMEs for rapiddecrease, as is typical of active regions, and to slow CMEs for gentledecrease, as is typical of the quiet Sun. Complex (quadrupolar) active regionslead to the fastest CMEs.

Author: T. Toeroek, B. Kliem


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