Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS data is selected as the forecasted time. We then validated the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereas that of MHD simulations without IPS data, in which the initial CME speed is derived from white-light coronagraph images, is approximately 6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrival times are earlier than the actual arrival times. These early predictions may be due to overestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

中文翻译：

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基于行星际闪烁观测的磁流体动力学模拟验证日冕物质抛射到达时间预测

日冕物质抛射（CME）对空间环境造成各种扰动；因此，预测他们的到达时间非常重要。然而，CME 在行星际空间的有限观测阻碍了预测的准确性。本研究调查了通过基于行星际闪烁 (IPS) 观测的三维 (3D) 磁流体动力学 (MHD) 模拟预测的 CME 到达地球时间的准确性。在该系统中，CME 近似为具有各种初始速度的球体。测试了具有不同 CME 初始速度的十次 MHD 模拟，并将每次模拟运行得出的密度分布与名古屋大学天地环境研究所 (ISEE) 观测到的 IPS 数据进行比较。选择与 IPS 数据最接近的模拟运行的 CME 到达时间作为预测时间。然后，我们使用 12 个晕 CME 事件验证了该预测的准确性。基于 IPS 的 MHD 预测的平均绝对到达时间误差约为 5.0 小时，这是有史以来最准确的预测之一，而没有 IPS 数据的 MHD 模拟的平均绝对到达时间误差来自于白光日冕图像，大约是 6.7 小时。这表明将 IPS 数据同化到 MHD 模拟中可以提高 CME 到达时间预测的准确性。平均预计到达时间早于实际到达时间。