标题： 在预测日冕物质抛射中的 Bz 时，哪些上游太阳风条件最为重要 显示英文标题

标题： Which Upstream Solar Wind Conditions Matter Most in Predicting Bz within Coronal Mass Ejections

摘要： 准确预测行星际磁场的 z 分量（特别是在行星际日冕物质抛射（ICME）通过期间）是空间天气预报的关键目标。目前，仅有少量技术被提出，但它们的范围和准确性仍然有限。最近，开发了一种稳健的机器学习（ML）技术，用于基于一组 42 个“特征”（即从 ICME 上游及其鞘区测量值计算出的变量）预测 ICME 内 Bz 的最小值。 在这项研究中，我们更详细地调查了这些所谓的解释变量，重点关注那些（1）统计上显著；以及（2）最重要的变量。我们发现，数密度和磁场强度占了大部分的变化比例。这些特征捕捉到了 ICME 对前方太阳风压缩的程度。直观上，这很有道理：当日冕物质抛射（CME）爆发时，释放的能量被分配为磁能和动能。因此，更强大的 CME 以更大的磁通绳场（更大的 Bz）、更高的速度发射，导致更多的鞘区压缩（增加的数密度和总场强）。 显示英文摘要

摘要： Accurately predicting the z-component of the interplanetary magnetic field, particularly during the passage of an interplanetary coronal mass ejection (ICME), is a crucial objective for space weather predictions. Currently, only a handful of techniques have been proposed and they remain limited in scope and accuracy. Recently, a robust machine learning (ML) technique was developed for predicting the minimum value of Bz within ICMEs based on a set of 42 'features', that is, variables calculated from measured quantities upstream of the ICME and within its sheath region. In this study, we investigate these so-called explanatory variables in more detail, focusing on those that were (1) statistically significant; and (2) most important. We find that number density and magnetic field strength accounted for a large proportion of the variability. These features capture the degree to which the ICME compresses the ambient solar wind ahead. Intuitively, this makes sense: Energy made available to CMEs as they erupt is partitioned into magnetic and kinetic energy. Thus, more powerful CMEs are launched with larger flux-rope fields (larger Bz), at greater speeds, resulting in more sheath compression (increased number density and total field strength).