Abstract
AbstractPredictions of the arrival of four coronal mass ejections (CMEs) in geospace are produced through use of three CME geometric models combined with CME drag modeling, constraining these models with the available Coronagraph and Heliospheric Imager data. The efficacy of these predications is assessed by comparison with the Space Weather Prediction Center (SWPC) numerical MHD forecasts of these same events. It is found that such a prediction technique cannot outperform the standard SWPC forecast at a statistically meaningful level. We test the Harmonic Mean, Self‐Similar Expansion, and Ellipse Evolution geometric models, and find that, for these events at least, the differences between the models are smaller than the observational errors. We present a new method of characterizing CME fronts in the Heliospheric Imager field of view, utilizing the analysis of citizen scientists working with the Solar Stormwatch project, and we demonstrate that this provides a more accurate representation of the CME front than is obtained by experts analyzing elongation time maps for the studied events. Comparison of the CME kinematics estimated independently from the STEREO‐A and STEREO‐B Heliospheric Imager data reveals inconsistencies that cannot be explained within the observational errors and model assumptions. We argue that these observations imply that the assumptions of the CME geometric models are routinely invalidated and question their utility in a space weather forecasting context. These results argue for the continuing development of more advanced techniques to better exploit the Heliospheric Imager observations for space weather forecasting.
Highlights
Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the solar atmosphere into the solar wind
We have demonstrated that there are inconsistencies with the coronal mass ejections (CMEs) kinematics derived from the geometrical modeling of the studied events, we still considered it appropriate to test whether using these kinematics estimates in conjunction with a drag-based model (DBM), in a manner similar to ElEvoHi, could provide useful CME arrival time predictions
Throughout this report we have demonstrated that inconsistent results are obtained for the kinematics of CMEs estimated through the application of CME geometric models to ε-t profiles extracted from Heliospheric Imagers (HIs) data, at least for the four events that form the basis of this study
Summary
Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the solar atmosphere into the solar wind. The SSE model has been extended further to consider the CME front as elliptical rather than circular, introducing the ellipse aspect ratio as an additional free parameter, resulting in the ElCon model [Rollett et al, 2016] All these techniques, to date, have relied on estimating the propagation of a CME based on elongation time (ε-t) profiles extracted, generally manually from “J-maps.”. The SECCHI package on each of STA and STB includes the HI instrument [Eyles et al, 2008], which consists of two wide-field white-light cameras (HI1 and HI2) that can image solar wind structures such as CMEs propagating over a total elongation angle range from near 4∘ to around 90∘ from the Sun. In nominal science operations, the 20∘ FOV of HI1 is centered at 14∘ in the ecliptic plane and the 70∘ FOV of HI2 is centered at 53.8∘, in the ecliptic plane. Throughout this work we will discuss the location of features in the HI FOV in terms of Helioprojective-Radial-Coordinates: position angle (PA), the anticlockwise angle from solar north, and elongation (ε), the angular distance from Sun center
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