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

TL;DR

This study investigates how magnetic reconnection influences both the acceleration and expansion of a coronal mass ejection in the high corona, revealing that reconnection contributes significantly to both processes.

Contribution

It provides a detailed analysis of a CME showing that magnetic reconnection plays a key role in its acceleration and expansion, with comparable effects on both.

Findings

Magnetic reconnection occurs after CME eruption and continues during propagation.

Reconnection contributes nearly equally to CME acceleration and expansion.

True CME acceleration is comparable to radial expansion, both influenced by reconnection.

Abstract

The important role played by magnetic reconnection in the early acceleration of coronal mass ejections (CMEs) has been widely discussed. However, as CMEs may have expansion speeds comparable to their propagation speeds in the corona, it is not clear whether and how reconnection contributes to the true acceleration and expansion separately. To address this question, we analyze the dynamics of a moderately fast CME on 2013 February 27, associated with a continuous acceleration of its front into the high corona, even though its speed 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 the radial direction. The CME true acceleration, i.e., the acceleration of its center, is then estimated by taking into account the expected deceleration caused by the solar wind drag force acting on a fast CME. It is found that the true acceleration and the radial expansion have similar magnitudes. We find that magnetic reconnection occurs after the CME eruption and continues during the CME propagation in the high corona, which contributes to the CME dynamic evolution. Comparison between the apparent acceleration related to the expansion and the true acceleration that compensates the drag shows that, for this case, magnetic reconnection contributes almost equally to the CME expansion and to the CME acceleration. The consequences of these measurements for the evolution of CMEs as they transit from the corona to the heliosphere are discussed.