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The important role played by magnetic reconnection in the early accelerationof coronal mass ejections (CMEs) has been widely discussed. However, as CMEsmay have expansion speeds comparable to their propagation speeds in the corona,it is not clear whether and how reconnection contributes to the trueacceleration and expansion separately. To address this question, we analyze thedynamics of a moderately fast CME on 2013 February 27, associated with acontinuous acceleration of its front into the high corona, even though itsspeed had reached $\sim$700~km~s$^{-1}$ and larger than the solar wind speed.The apparent CME acceleration is found to be due to the CME expansion in theradial direction. The CME true acceleration, i.e., the acceleration of itscenter, is then estimated by taking into account the expected decelerationcaused by the solar wind drag force acting on a fast CME. It is found that thetrue acceleration and the radial expansion have similar magnitudes. We findthat magnetic reconnection occurs after the CME eruption and continues duringthe CME propagation in the high corona, which contributes to the CME dynamicevolution. Comparison between the apparent acceleration related to theexpansion and the true acceleration that compensates the drag shows that, forthis case, magnetic reconnection contributes almost equally to the CMEexpansion and to the CME acceleration. The consequences of these measurementsfor the evolution of CMEs as they transit from the corona to the heliosphereare discussed.

Acceleration and Expansion of a Coronal Mass Ejection in the High Corona: Role of Magnetic Reconnection