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Register a new userA STEREO Survey of Magnetic Cloud Coronal Mass Ejections Observed at Earth in 2008--2012
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We identify coronal mass ejections (CMEs) associated with magnetic clouds (MCs) observed near Earth by the Wind spacecraft from 2008 to mid-2012, a time period when the two STEREO spacecraft were well positioned to study Earth-directed CMEs. We find 31 out of 48 Wind MCs during this period can be clearly connected with a CME that is trackable in STEREO imagery all the way from the Sun to near 1 AU. For these events, we perform full 3-D reconstructions of the CME structure and kinematics, assuming a flux rope morphology for the CME shape, considering the full complement of STEREO and SOHO imaging constraints. We find that the flux rope orientations and sizes inferred from imaging are not well correlated with MC orientations and sizes inferred from the Wind data. However, velocities within the MC region are reproduced reasonably well by the image-based reconstruction. Our kinematic measurements are used to provide simple prescriptions for predicting CME arrival times at Earth, provided for a range of distances from the Sun where CME velocity measurements might be made. Finally, we discuss the differences in the morphology and kinematics of CME flux ropes associated with different surface phenomena (flares, filament eruptions, or no surface activity).
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A sample of isolated Earth-impacting ICMEs that occurred in the period January 2008 to August 2014 is analysed in order to study in detail the ICME in situ signatures with respect to the type of filament eruption related to the corresponding CME. For Earth-directed CMEs, a kinematical study was performed using the STEREO-A, B COR1 and COR2 coronagraphs and the Heliospheric Imagers HI1. Based on the extrapolated CME kinematics, we identified interacting CMEs, which were excluded from further analysis. Applying this approach, a set of 31 isolated Earth-impacting CMEs was unambiguously identified and related to the in situ measurements recorded by the Wind spacecraft. We classified the events into subsets with respect to the CME source location as well as with respect to the type of the associated filament eruption. Hence, the events are divided into three subsamples: active region (AR) CMEs, disappearing filament (DSF) CMEs, and stealthy CMEs. The related three groups of ICMEs were further divided into two subsets: magnetic obstacle (MO) events (out of which four were stealthy), covering ICMEs that at least partly expose characteristics of flux ropes, and ejecta (EJ) events, not showing such characteristics. In the next step, MO-events were analysed in more detail, considering the magnetic field strengths and the plasma characteristics in three different segments of the ICMEs, defined as the turbulent sheath (TS), the frontal region (FR), and the MO itself. The analysis revealed various well-defined correlations for AR, DSF, and stealthy ICMEs, which we interpreted considering basic physical concepts. Our results support the hypothesis that ICMEs show different signatures depending on the in situ spacecraft trajectory, in terms of apex versus flank hits.
The process by which the Sun affects the terrestrial environment on short timescales is predominately driven by the amount of magnetic reconnection between the solar wind and Earths magnetosphere. Reconnection occurs most efficiently when the solar wind magnetic field has a southward component. The most severe impacts are during the arrival of a coronal mass ejection (CME) when the magnetosphere is both compressed and magnetically connected to the heliospheric environment. Unfortunately, forecasting magnetic vectors within coronal mass ejections remains elusive. Here we report how, by combining a statistically robust helicity rule for a CMEs solar origin with a simplified flux rope topology the magnetic vectors within the Earth-directed segment of a CME can be predicted. In order to test the validity of this proof-of-concept architecture for estimating the magnetic vectors within CMEs, a total of eight CME events (between 2010 and 2014) have been investigated. With a focus on the large false alarm of January 2014, this work highlights the importance of including the early evolutionary effects of a CME for forecasting purposes. The angular rotation in the predicted magnetic field closely follows the broad rotational structure seen within the in situ data. This time-varying field estimate is implemented into a process to quantitatively predict a time-varying Kp index that is described in detail in paper II. Future statistical work, quantifying the uncertainties in this process, may improve the more heuristic approach used by early forecasting systems.
Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with coronal mass ejections (CMEs). Recent study found that coronal dimming is the only signature that could differentiate powerful ares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we first demonstrate the capability of the model to reproduce solar observations. We then extend the model for simulating stellar CMEs by modifying the input magnetic flux density as well as the initial magnetic energy of the CME flux rope. Our result suggests that with improved instrument sensitivity, it is possible to detect the coronal dimming signals induced by the stellar CMEs.
Our study attempts to understand the collision characteristics of two coronal mass ejections (CMEs) launched successively from the Sun on 2013 October 25. The estimated kinematics, from three-dimensional (3D) reconstruction techniques applied to observations of CMEs by SECCHI/Coronagraphic (COR) and Heliospheric Imagers (HIs), reveal their collision around 37 $R_sun$ from the Sun. In the analysis, we take into account the propagation and expansion speeds, impact direction, angular size as well as the masses of the CMEs. These parameters are derived from imaging observations, but may suffer from large uncertainties. Therefore, by adopting head-on as well as oblique collision scenarios, we have quantified the range of uncertainties involved in the calculation of the coefficient of restitution for expanding magnetized plasmoids. Our study shows that the comparatively large expansion speed of the following CME than that of the preceding CME, results in a higher probability of super-elastic collision. We also infer that a relative approaching speed of the CMEs lower than the sum of their expansion speeds increases the chance of super-elastic collision. The analysis under a reasonable errors in observed parameters of the CME, reveals the larger probability of occurrence of an inelastic collision for the selected CMEs. We suggest that the collision nature of two CMEs should be discussed in 3D, and the calculated value of the coefficient of restitution may suffer from a large uncertainty.
This study aims to provide a reference to different magnetic field models and reconstruction methods for interplanetary coronal mass ejections (ICMEs). In order to understand the differences in the outputs of those models and codes, we analyze 59 events from the Coordinated Data Analysis Workshop (CDAW) list, using four different magnetic field models and reconstruction techniques; force-free fitting (Goldstein,1983,Burlaga,1988,Lepping et al.,1990), magnetostatic reconstruction using a numerical solution to the Grad-Shafranov equation (Hu and Sonnerup, 2001), fitting to a self-similarly expanding cylindrical configuration (Marubashi and Lepping, 2007) and elliptical, non-force free fitting (Hidalgo,2003). The resulting parameters of the reconstructions for the 59 events are compared statistically, as well as in selected case studies. The ability of a method to fit or reconstruct an event is found to vary greatly: the Grad-Shafranov reconstruction is successful for most magnetic clouds (MCs) but for less than 10% of the non-MC ICMEs; the other three methods provide a successful fit for more than 65% of all events. The differences between the reconstruction and fitting methods are discussed, and suggestions are proposed as to how to reduce them. We find that the magnitude of the axial field is relatively consistent across models but not the orientation of the axis of the ejecta. We also find that there are a few cases for which different signs of the magnetic helicity are found for the same event when we do not fix the boundaries, illustrating that this simplest of parameters is not necessarily always well constrained by fitting and reconstruction models. Finally, we look at three unique cases in depth to provide a comprehensive idea of the different aspects of how the fitting and reconstruction codes work.
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