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Register a new userSun-to-Earth Observations and Characteristics of Isolated Earth-Impacting Interplanetary Coronal Mass Ejections During 2008-2014
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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.
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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).
In order to have a comprehensive view of the propagation and evolution of coronal mass ejections (CMEs) from the Sun to deep interplanetary space beyond 1 au, we carry out a kinematic analysis of 7 CMEs in solar cycle 23. The events are required to have coordinated coronagraph observations, interplanetary type II radio bursts, and multi-point in-situ measurements at the Earth and Ulysses. A graduated cylindrical shell model, an analytical model without free parameters and a magnetohydrodynamic model are used to derive CME kinematics near the Sun, to quantify the CME/shock propagation in the Sun-Earth space, and to connect in-situ signatures at the Earth and Ulysses, respectively. We find that each of the 7 CME-driven shocks experienced a major deceleration before reaching 1 au and thereafter propagated with a gradual deceleration from the Earth to larger distances. The resulting CME/shock propagation profile for each case is roughly consistent with all the data, which verifies the usefulness of the simple analytical model for CME/shock propagation in the heliosphere. The statistical analysis of CME kinematics indicates a tendency that the faster the CME, the larger the deceleration, and the shorter the deceleration time period within 1 au. For several of these events, the associated geomagnetic storms were mainly caused by the southward magnetic fields in the sheath region. In particular, the interaction between a CME-driven shock and a preceding ejecta significantly enhanced the preexisting southward magnetic fields and gave rise to a severe complex geomagnetic storm.
Coronal Mass Ejections (CMEs) are large-scale eruptions from the Sun into interplanetary space. Despite being major space weather drivers, our knowledge of the CME properties in the inner heliosphere remains constrained by the scarcity of observations at distances other than 1 au. Furthermore, most CMEs are observed in situ by single spacecraft, requiring numerical models to complement the sparse observations available. We aim to assess the ability of the linear force-free spheromak CME model in EUHFORIA to describe the radial evolution of interplanetary CMEs, yielding new context for observational studies. We model one well-studied CME, and investigate its radial evolution by placing virtual spacecraft along the Sun-Earth line in the simulation domain. To directly compare observational and modelling results, we characterise the interplanetary CME signatures between 0.2 and 1.9 au from modelled time series, exploiting techniques traditionally employed to analyse real in situ data. Results show that the modelled radial evolution of the mean solar wind and CME values is consistent with observational and theoretical expectations. The CME expands as a consequence of the decaying pressure in the surrounding wind: the expansion is rapid within 0.4 au, and moderate at larger distances. The early rapid expansion could not explain the overestimated CME radial size in our simulation, suggesting this is an intrinsic limitation of the spheromak geometry used. The magnetic field profile indicates a relaxation of the CME during propagation, while ageing is most probably not a substantial source of magnetic asymmetry beyond 0.4 au. We also report a CME wake that is significantly shorter than suggested by observations. Overall, EUHFORIA provides a consistent description of the radial evolution of solar wind and CMEs; nevertheless, improvements are required to better reproduce the CME radial extension.
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.
We compare the magnetic helicity in the 17-18 March 2013 interplanetary coronal mass ejection (ICME) flux-rope at 1 AU and in its solar counterpart. The progenitor coronal mass ejection (CME) erupted on 15 March 2013 from NOAA active region 11692 and associated with an M1.1 flare. We derive the source region reconnection flux using post-eruption arcade (PEA) method (Gopalswamy et al. 2017a) that uses the photospheric magnetogram and the area under the PEA. The geometrical properties of the near-Sun flux rope is obtained by forward-modeling of white-light CME observations. Combining the geometrical properties and the reconnection flux we extract the magnetic properties of the CME flux rope (Gopalswamy et al. 2017b). We derive the magnetic helicity of the flux rope using its magnetic and geometric properties obtained near the Sun and at 1 AU. We use a constant-{alpha} force-free cylindrical flux rope model fit to the in situ observations in order to derive the magnetic and geometric information of the 1-AU ICME. We find a good correspondence in both amplitude and sign of the helicity between the ICME and the CME assuming a semi-circular (half torus) ICME flux rope with a length of {pi} AU. We find that about 83% of the total flux rope helicity at 1 AU is injected by the magnetic reconnection in the low corona. We discuss the effect of assuming flux rope length in the derived value of the magnetic helicity. This study connecting the helicity of magnetic flux ropes through the Sun-Earth system has important implications for the origin of helicity in the interplanetary medium and the topology of ICME flux ropes at 1 AU and hence their space weather consequences.
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