Forces governing coronal mass ejections

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.