Severe geomagnetic storms are driven by the coronal mass ejections (CMEs). Consequently, there has been a great deal of focus on predicting if and when a CME will arrive in near‐Earth space. However, it is useful to step back and ask, “How valuable is this information, in isolation, for making decisions to mitigate against the adverse effects of space weather?” While all severe geomagnetic storms are triggered by CMEs, not all CMEs trigger severe storms. Thus, even perfect knowledge of CME arrival time will provide “actionable” forecast information only in operational situations where false alarms can be tolerated. Of course, any CME transit model used to predict CME arrival time must also produce an estimate of CME speed at Earth. This can help discriminate between geoeffective and nongeoeffective CMEs, reducing false alarms and expanding the range of operational scenarios under which a forecast provides value. Thus, from an end‐user perspective, CME arrival speed should form part of the standard metric by which CME transit models are evaluated. Looking to the future, even coarse information about the CME magnetic properties would likely provide even greater forecast value. These points are illustrated by a simple analysis of solar wind data.

中文翻译：

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CME到达时间预测对减轻空间天气的价值

严重的地磁风暴是由日冕物质抛射（CME）驱动的。因此，人们非常关注预测CME是否以及何时到达近地空间。但是，退后一步来问：“这些信息在孤立地制定决策以减轻空间天气的不利影响时有多有价值？” 尽管所有严重的地磁风暴都是由CME触发的，但并非所有的CME都会触发严重的风暴。因此，即使对CME到达时间的全面了解，也仅在可以容忍错误警报的操作情况下才能提供“可操作的”预测信息。当然，用于预测CME到达时间的任何CME传输模型也必须产生对地球CME速度的估计。这可以帮助区分地球有效和非地球有效的CME，减少误报并扩大预测可提供价值的操作方案的范围。因此，从最终用户的角度来看，CME到达速度应成为评估CME运输模型的标准指标的一部分。展望未来，即使有关CME磁性能的粗略信息也可能会提供更大的预测价值。这些点通过对太阳风数据的简单分析得到说明。