Near‐Sun speed of CMEs and the magnetic nonpotentiality of their source active regions

We show that the speed of the fastest coronal mass ejections (CMEs) that an active region (AR) can produce can be predicted from a vector magnetogram of the AR. This is shown by logarithmic plots of CME speed (from the SOHO Large Angle and Spectrometric Coronagraph CME catalog) versus each of ten AR‐integrated magnetic parameters (AR magnetic flux, three different AR magnetic‐twist parameters, and six AR free‐magnetic‐energy proxies) measured from the vertical and horizontal field components of vector magnetograms (from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager) of the source ARs of 189 CMEs. These plots show the following: (1) the speed of the fastest CMEs that an AR can produce increases with each of these whole‐AR magnetic parameters and (2) that one of the AR magnetic‐twist parameters and the corresponding free‐magnetic‐energy proxy each determine the CME‐speed upper limit line somewhat better than any of the other eight whole‐AR magnetic parameters.