约束调和平均法求解ICME动力学的数值模拟
Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation
摘要：
在这项研究中，我们使用一个人工日冕物质抛射（CME）的数值模拟来验证一种计算行星际CME（ICME）传播方向和运动学轮廓的方法。在这种方法中，从日光层图像的观测与现场等离子体和现场数据在1 AU的约束。这些数据用于通过应用假设ICME前沿的球形形状的调和平均方法将测量的ICME伸长转换为距离。我们使用合成白光图像，类似于STEREO-A/HI观察到的，远程和原位航天器之间的三个不同的分离角，30°，60°和90°。为了验证该方法的结果，将它们与从顶视图获得的建模ICME的顶点速度曲线进行比较。该轮廓反映了“真实”顶点运动学，因为它不受散射或投影效应的影响。以这种方式，可以确定用于揭示ICME传播方向和运动学的方法的精度。我们发现，通过约束调和平均法获得的方向对分离角不是很敏感（30° sep：θ = W7; 60° sep：θ = W12; 90° sep：θ = W15;真实方向：E0/W0）。对于所有三种情况下，推导的运动学是在一个相对较好的协议与真正的运动学。随着分离角的增大，1AU处的ICME速度越来越被高估（30° sep：ΔV_s ~-50 km/s，60° sep：Δ V_s ~+75 km/s，90° sep：ΔV_s ~+125 km/s）。特别是对于未来的L4/L5飞行任务来说，60°分离情况对于改进空间天气预报是非常有意义的。
英文摘要：
In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the Harmonic Mean approach that assumes a spherical shape of the ICME front. We use synthetic white-light images, similar as observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft, of 30°, 60°, and 90°. To validate the results of the method they are compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the "true" apex kinematics since it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained Harmonic Mean method is not very sensitive to the separation angle (30° sep: ϕ= W7; 60° sep: ϕ= W12; 90° sep: ϕ= W15; true dir.: E0/W0). For all three cases the derived kinematics are in a relatively good agreement with the real kinematics. The best consistency is obtained for the 30° case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30° sep: ΔV_arr ~-50 km/s, 60° sep: ΔV_arr ~+75 km/s, 90° sep: ΔV_arr ~+125 km/s). Especially for future L4/L5 missions the 60° separation case is highly interesting in order to improve space weather forecasts.
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