Paper detail

Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation

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.