Interplanetary coronal mass ejections (ICMEs) primarily move radially as they propagate away from the Sun, maintaining approximately constant angular width with respect to the Sun. As ICMEs have typical angular widths of around $60^{\circ }$ , plasma elements on opposite flanks of an ICME separate in the non-radial direction at a speed, $v_{\mathrm{G}}$ , roughly equal to the ICME radial speed. This rapid expansion is a limiting factor on the propagation of information across an ICME at the local Alfven speed, $v_{\mathrm{A}}$ . In this study, the 1-AU properties of ICMEs are used to compute two measures of ICME coherence. The first is the angular separation for which $v_{\mathrm{G}}$ exceeds the local $v_{\mathrm{A}}$ . The second measure is the angular extent over which a wavefront can propagate as an ICME travels from a given heliocentric distance to 1 AU. For both measures, ICMEs containing magnetic clouds show greater coherence than non-cloud ICMEs. However, even for magnetic clouds, information is unable to propagate across the full span of the structure. Thus interactions of ICMEs with other solar wind structures in the heliosphere are likely to lead to localised distortion, rather than solid-body like deflection. For magnetic clouds, the coherence length scale is significantly greater near the centre of the spacecraft encounter than at the leading or trailing edges. This suggests that magnetic clouds may be more coherent, and thus less prone to distortion, along the direction of the magnetic flux-rope axis than in directions perpendicular to the axis.

中文翻译：

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近地空间日冕物质抛射的相干性

行星际日冕物质抛射 (ICME) 主要是在远离太阳传播时径向移动，相对于太阳保持大致恒定的角宽度。由于 ICME 具有大约 $60^{\circ }$ 的典型角宽度，因此 ICME 相对侧翼上的等离子体元素以 $v_{\mathrm{G}}$ 的速度在非径向方向上分离，大致等于ICME 径向速度。这种快速扩展是信息以本地 Alfven 速度 $v_{\mathrm{A}}$ 跨 ICME 传播的限制因素。在这项研究中，ICME 的 1-AU 属性用于计算 ICME 相干性的两个度量。第一个是 $v_{\mathrm{G}}$ 超过局部 $v_{\mathrm{A}}$ 的角间距。第二个度量是当 ICME 从给定的日心距离传播到 1 AU 时波前可以传播的角度范围。对于这两种测量，包含磁云的 ICME 比非云 ICME 显示出更大的相干性。然而，即使对于磁云，信息也无法在结构的整个跨度上传播。因此，ICME 与日光层中其他太阳风结构的相互作用可能会导致局部变形，而不是像固体一样的偏转。对于磁云，航天器相遇中心附近的相干长度尺度明显大于前缘或后缘。这表明磁云沿着磁通绳轴的方向可能比在垂直于轴的方向上更连贯，因此更不容易变形。