A proper characterization of the kinematics of coronal mass ejections (CMEs) is important not only for practical purposes, i.e. space weather forecasting, but also to improve our current understanding of the physics behind their evolution in the middle corona and into the heliosphere. The first and core step toward this goal is the estimation of the three main components of the CME speeds, namely the expansion speed relative to the center of motion in both, the radial and lateral directions, and the propagation speed (i.e. $V_{\mathrm{front}}$ , $V_{\mathrm{lat}}$ , $V_{\mathrm{bulk}}$ , respectively). To this aim, we exploit the observations obtained with COR2 onboard the Solar Terrestrial Relations Observatory (STEREO) from 2007 to 2014 to investigate the relationships among the different components as a function of the heliocentric distance of the CME events. Here, we analyze a sample of 475 CMEs. The selected events exhibit clear flux rope signatures as seen either edge on (i.e. F-CMEs: three-part structure, presence of a cavity) or face on (i.e. L- or loop CMEs) in white light images. Our main findings are: i) L-CMEs show almost twice as large expansion speeds compared to F-CMEs ( $V_{\mathrm {front},\mathrm{L}}=367~\mbox{km}\,\mbox{s}^{-1}$ , $V_{\mathrm{lat},\mathrm{L}}=365~\mbox{km}\,\mbox{s}^{-1}$ vs. $V_{\mathrm{front},\mathrm{F}}=215~\mbox{km}\,\mbox{s}^{-1}$ , $V_{\mathrm{lat},\mathrm{F}}= 182~\mbox{km}\,\mbox{s}^{-1}$ ); ii) the relationship between the two components of the expansion speeds is linear and does not change with height; iii) the ratio of the propagation speed to the lateral expansion speed is a function of the angular width that describes the self-similarity evolution of a CME; and iv) 65% of the CMEs exhibit a self-similar evolution at 10 solar radii, reaching 70% at 15 solar radii.

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关于日冕物质抛射的扩张速度：自相似演化的启示

对日冕物质抛射 (CME) 运动学的正确表征不仅对于实际目的（即空间天气预报）很重要，而且对于提高我们目前对日冕中部和日光层演化背后的物理学的理解也很重要。实现这一目标的第一步也是核心步骤是估计 CME 速度的三个主要组成部分，即相对于运动中心在径向和横向方向上的膨胀速度，以及传播速度（即 $V_{\ mathrm{front}}$ 、 $V_{\mathrm{lat}}$ 、 $V_{\mathrm{bulk}}$ ）。为了这个目标，我们利用 COR2 在 2007 年至 2014 年间在日地关系天文台 (STEREO) 上获得的观测结果来研究不同组件之间的关系，作为 CME 事件的日心距离的函数。在这里，我们分析了 475 个 CME 的样本。所选事件表现出清晰的通量绳特征，如在白光图像中的边缘（即 F-CME：三部分结构，存在空腔）或面（即 L 或环形 CME）所见。我们的主要发现是：i) L-CME 的扩展速度几乎是 F-CME 的两倍 ( $V_{\mathrm {front},\mathrm{L}}=367~\mbox{km}\,\mbox {s}^{-1}$ , $V_{\mathrm{lat},\mathrm{L}}=365~\mbox{km}\,\mbox{s}^{-1}$ vs. $V_ {\mathrm{front},\mathrm{F}}=215~\mbox{km}\,\mbox{s}^{-1}$ , $V_{\mathrm{lat},\mathrm{F}} = 182~\mbox{km}\,\mbox{s}^{-1}$ ); ii) 膨胀速度的两个分量之间呈线性关系，不随高度变化；iii) 传播速度与横向扩展速度的比值是描述 CME 自相似演化的角宽度的函数；iv) 65% 的 CME 在 10 个太阳半径处表现出自相似演化，在 15 个太阳半径处达到 70%。