Shocks inside CMEs: A survey of properties from 1997 to 2006
Shocks inside CMEs: A survey of properties from 1997 to 2006
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DOI：
10.1002/2014ja020848
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
N. Lugaz;C. Farrugia;Charles W. Smith;K. Paulson
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文献类型：
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作者：
N. Lugaz;C. Farrugia;Charles W. Smith;K. Paulson
我们报告了 1997 年至 2006 年期间通过 Wind 和 ACE 在 1 个天文单位测量到的 49 个在日冕物质抛射 (CME) 内传播的快速模式前向激波。与典型的 CME 驱动的激波相比，这些激波在不同的上游条件下传播，其中上游阿尔文速度中值为 85 km s−1，质子 β = 0.08，磁场强度为 8 nT。这些冲击速度很快，中值速度为 590 km s−1，但很弱，中值阿尔芬尼马赫数为 1.9。它们通常将磁场和密度压缩 2-3 倍。发现的最极端的上游条件是 230 km s−1 的快磁声速、0.02 的等离子体 β、740 km s−1 的上游太阳风速度和 0.5 cm−3 的密度。其中 19 个复杂事件与 Wind 冲击检测后 12 小时内的强烈地磁风暴（峰值 Dst 低于 -100 nT）有关，15 个事件与冲击检测后 3 至 9 小时内风暴时间 Dst 指数下降超过 50 nT 有关。我们还将它们与在更典型的上游条件下传播的 45 个冲击样本进行了比较。我们通过叠加历元分析展示了这些激波的平均特性，并提出了一些关于低 β 状态中激波压缩比的分析考虑。由于大多数激波是在日冕物质抛射的后半部分测量的，我们得出的结论是，由于上游和磁声速较大，当它们传播到整个日冕物质抛射时，大约一半的激波可能不会保持快速模式激波。
We report on 49 fast‐mode forward shocks propagating inside coronal mass ejections (CMEs) as measured by Wind and ACE at 1 AU from 1997 to 2006. Compared to typical CME‐driven shocks, these shocks propagate in different upstream conditions, where the median upstream Alfvén speed is 85 km s−1, the proton β = 0.08 and the magnetic field strength is 8 nT. These shocks are fast with a median speed of 590 km s−1 but weak with a median Alfvénic Mach number of 1.9. They typically compress the magnetic field and density by a factor of 2–3. The most extreme upstream conditions found were a fast magnetosonic speed of 230 km s−1, a plasma β of 0.02, upstream solar wind speed of 740 km s−1 and density of 0.5 cm−3. Nineteen of these complex events were associated with an intense geomagnetic storm (peak Dst under −100 nT) within 12 h of the shock detection at Wind, and 15 were associated with a drop of the storm time Dst index of more than 50 nT between 3 and 9 h after shock detection. We also compare them to a sample of 45 shocks propagating in more typical upstream conditions. We show the average property of these shocks through a superposed epoch analysis, and we present some analytical considerations regarding the compression ratios of shocks in low β regimes. As most of these shocks are measured in the back half of a CME, we conclude that about half the shocks may not remain fast‐mode shocks as they propagate through an entire CME due to the large upstream and magnetosonic speeds.