The interaction of interplanetary coronal mass ejections (ICME) with each other and with co-rotating interaction regions (CIR) changes their configuration, dynamics, magnetic field and plasma characteristics and can make space weather forecasting difficult. During the period of March 20–25, 2011, the Solar Terrestrial Relation Observatory ( STEREO B) encountered a compound stream containing several interacting structures. Our analysis suggests that the stream consists of two ICMEs followed by an embedded ICME/CIR. The sudden appearance of the third ICME within the fast wind side of the CIR causes the proton temperature( T p $T_{p} $ ) to drop suddenly to its lowest level in about 1.2 hours, from 3.89 × 10 5 $3.89 \times 10^{5}$ K to 1.07 × 10 4 $1.07 \times 10^{4}$ K (by a factor of ≈36). The fast wind which follows the CIR influences not only the third ICME’s temperature but also its proton beta ( β p $\upbeta_{\mathrm{p}}$ ). In addition, the third ICME impacts the CIR through expansion and deceleration. A forward pressure wave penetrates ICME1. It’s source is either the second ICME, the merged third ICME and CIR, or it may be a remnant shock. The compression causes an increase of the T p $T_{p}$ and β p $\upbeta_{\mathrm{p}}$ of the second and part of the first ICME. Despite the signatures of four large-scale interacting structures within the compound stream, it is difficult to reconcile the in-situ sequence with other remote sensing observations of ejecta close to the Sun because of the large system of coronal expanding loops above the active region. Compound streams therefore remain difficult to interpret, and further understanding of the subject will depend on the future study of similar events.

中文翻译：

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STEREO B航天器测得的2011年3月20-25日复合流事件

行星际日冕物质抛射 (ICME) 之间的相互作用以及与同向旋转相互作用区 (CIR) 的相互作用改变了它们的配置、动力学、磁场和等离子体特性，并可能使空间天气预报变得困难。在 2011 年 3 月 20 日至 25 日期间，日地关系天文台 (STEREO B) 遇到了包含多个相互作用结构的复合流。我们的分析表明，该流由两个 ICME 和一个嵌入式 ICME/CIR 组成。在 CIR 快风侧突然出现第三个 ICME 导致质子温度 (T p $T_{p} $ ) 在大约 1.2 小时内突然下降到最低水平，从 3.89 × 10 5 $3.89 \times 10 ^{5}$ K 到 1.07 × 10 4 $1.07 \times 10^{4}$ K（乘以 ≈36）。跟随 CIR 的快风不仅影响第三个 ICME 的温度，而且影响它的质子 beta ( β p $\upbeta_{\mathrm{p}}$ )。此外，第三次 ICME 通过扩张和减速影响 CIR。前向压力波穿透 ICME1。它的来源要么是第二个 ICME、合并的第三个 ICME 和 CIR，要么可能是残余冲击。压缩导致第二个和第一个 ICME 的一部分的 T p $T_{p}$ 和 β p $\upbeta_{\mathrm{p}}$ 增加。尽管复合流内有四个大规模相互作用结构的特征，但由于活动区域上方的日冕膨胀环的大型系统，很难将原位序列与太阳附近喷射物的其他遥感观测相协调。因此，复合流仍然难以解释，