Modeling the Observed Distortion of Multiple (Ghost) CME Fronts in STEREO Heliospheric Imagers

Yutian Chi,Luke Barnard,Mike Lockwood,Mathew Owens,Matthew Lang,Chenglong Shen,Jie Zhang,Christopher Scott,Zhihui Zhong,Bingkun Yu,Yuming Wang,Shannon Jones,Mengjiao Xu

doi:10.3847/2041-8213/ac1203

Abstract

Abstract In this work we have, for the first time, applied the interpretation of multiple “ghost-fronts” to two synthetic coronal mass ejections (CMEs) propagating within a structured solar wind using the Heliospheric Upwind eXtrapolation time (HUXt) solar wind model. The two CMEs occurred on 2012 June 13–14 showing multiple fronts in images from Solar Terrestrial Relations Observatory Heliospheric Imagers (HIs). The HUXt model is used to simulate the evolution of these CMEs across the inner heliosphere as they interacted with structured ambient solar wind. The simulations reveal that the evolution of CME shape is consistent with observations across a wide range of solar latitudes and that the manifestation of multiple “ghost-fronts” within HIs’ field of view is consistent with the positions of the nose and flank of the same CME structure. This provides further confirmation that the angular separation of these features provides information on the longitudinal extent of a CME. For one of the CMEs considered in this study, both simulations and observations show that a concave shape develops within the outer CME front. We conclude that this distortion results from a latitudinal structure in the ambient solar wind speed. The work emphasizes that the shape of the CME cannot be assumed to remain a coherent geometrical shape during its propagation in the heliosphere. Our analysis demonstrates that the presence of “ghost” CME fronts can be used to infer the distortion of CMEs by ambient solar wind structure as a function of both latitude and longitude. This information has the potential to improve the forecasting of space weather events at Earth.

Highlights

Coronal mass ejections (CMEs) are spectacular eruptions of plasma and magnetic field transferring huge energies from the solar corona into the interplanetary medium
The purpose of this work is to investigate whether the interpretation of multiple fronts within a coronal mass ejections (CMEs) observed by Heliospheric Imagers (HIs) holds when considering the impact of a structured ambient solar wind
In this Letter, we perform a study on the evolution and propagation of two CMEs that erupted successively during 2012 June 13–14, combining the white light observations from Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO), and VEX and Wind in situ observations, and with the 3D Heliospheric Upwind eXtrapolation time (HUXt) model

Summary

Introduction

Coronal mass ejections (CMEs) are spectacular eruptions of plasma and magnetic field transferring huge energies from the solar corona into the interplanetary medium. Previous methods to interpret CMEs observations and predict their arrival time in near-Earth space have typically assumed a rigid and designated shape for the CME front during its propagation in the heliosphere (Sheeley et al 1999; Lugaz et al 2009; Sheeley & Rouillard 2010; Davies et al 2012) Such assumptions about the shape of CMEs are likely to be too simplistic when significant spatial gradients in the ambient solar wind conditions are present (Lugaz et al 2009; Barnard et al 2017).

Inserting and Tracking ICMEs in the Global HUXt Model

Discussion and Conclusion