Forces governing the take-off and propagation of CMEs

Bojan Vršnak 
Hvar Observatory, Faculty of Geodesy, Kačićeva 26, HR-10000 Zagreb, Croatia

Kinematics of CMEs is analyzed to get an insight into the properties of forces partaking in the 
eruption. It is demonstrated that the Lorentz force plays a dominant role within a distance of a 
few solar radii. In the distance range 1-30 solar radii, the inferred values of the Lorentz-force 
acceleration aL on average decrease with the heliocentric distance roughly as aL ? R-2. Generally, 
the values are found to be in the range g ? aL < 30g, where g(R) is the acceleration of gravity. 
In fast events, the aerodynamic drag is comparable to the Lorentz force, and on average also 
decreases with the distance. However, the decrease is more gradual, so the drag becomes essential 
in the upper corona and interplanetary space. 
Inspecting the CME-flare relationship it is demonstrated that the reconnection beneath the CME 
plays an active role in the CME acceleration. Statistically, the CME speeds are correlated with 
the importance of the associated flare. The distribution of non-flare CME speeds is very similar 
to that of CMEs associated with flares of the soft X-ray importance C, and includes a considerable 
fraction of fast events. This implies that the concept of two distinct classes of CMEs (flare and 
non-flare) should be reformulated.
It is proposed that the feedback relationship between the CME dynamics and the reconnection process 
in the wake of the CME is established during the CME take-off. The role of reconnection is to provide 
a "fresh" poloidal magnetic field to the flux rope, amplifying the kink-effect, and thus enhancing 
and prolonging the CME acceleration.

Work supported by Air Force Office of Scientific Research, USAF