Propagation Of Coronal Mass Ejections Research Articles

On the relationship between expansión angle of earth-directed CMES and soft X-ray emission from their related flare

In space weather, to study the impact of Earth-directed coronal mass ejections (CME) in our terrestrial environment, one of the most important parameters is the propagation speed of these disturbances. We present an improvement of the 3D CME Geometrical Propagation-Expansion Description (3D-CGPED) model developed in previous work to increase the simple that we can use in CME arrival time predictions. This 3D model estimates the arrival time of Earth-directed CMEs at Earth by including a 3D geometry for the CME propagation and expansion in interplanetary space. Since the 3D-CGPED model computes the expansion of the CME based on the radial distance of the CME front, only travel times for CMEs with welldefined shapes seen by coronographs can be estimated. In the present work, we found an empirical relationship between the expansion angle of CMEs with well-defined shapes and the start-to-peak SXR fluence of their associated flares. We applied this relationship in the 3D-CGPED model to obtain the expansion angle for 8 CMEs with an irregular shape. We found similar window errors in arrival time predictions compared to the previous work. This result allows us to complement the 3D-CGPED model to include not only regular shapes but also irregular ones for CMEs observed by coronographs in future works.

How Magnetic Erosion Affects the Drag-Based Kinematics of Fast Coronal Mass Ejections

In order to advance our understanding of the dynamic interactions between coronal mass ejections (CMEs) and the magnetized solar wind, we investigate the impact of magnetic erosion on the well-known aerodynamic drag force acting on CMEs traveling faster than the ambient solar wind. In particular, we start by generating empirical relationships for the basic physical parameters of CMEs that conserve their mass and magnetic flux. Furthermore, we examine the impact of the virtual mass on the equation of motion by studying a variable-mass system. We next implement magnetic reconnection into CME propagation, which erodes part of the CME magnetic flux and outer-shell mass, on the drag acting on CMEs, and we determine its impact on their time and speed of arrival at 1 AU. Depending on the strength of the magnetic erosion, the leading edge of the magnetic structure can reach near-Earth space up to ≈ three hours later, compared to the non-eroded case. Therefore, magnetic erosion may have a significant impact on the propagation of fast CMEs and on predictions of their arrivals at 1 AU. Finally, the modeling indicates that eroded CMEs may experience a significant mass decrease. Since such a decrease is not observed in the corona, the initiation distance of erosion may lie beyond the field-of-view of coronagraphs (i.e. 30~mathrm{R}_{odot }).

Trajectories of coronal mass ejection from solar-type stars

ABSTRACT The Sun and other solar-type stars have magnetic fields that permeate their interior and surface, extend through the interplanetary medium, and are the main drivers of stellar activity. Stellar magnetic activity affects the physical processes and conditions of the interplanetary medium and orbiting planets. Coronal mass ejections (CMEs) are the most impactful of these phenomena in near-Earth space weather and consist of plasma clouds with a magnetic field, ejected from the solar corona. Precisely predicting the trajectory of CMEs is crucial in determining whether a CME will hit a planet and impact its magnetosphere and atmosphere. Despite the rapid developments in the search for stellar CMEs, their detection is still very incipient. In this work, we aim to better understand the propagation of CMEs by analysing the influence of initial parameters on CME trajectories, such as position, velocities, and the stellar magnetic field’s configuration. We reconstruct magnetograms for Kepler-63 (KIC 11554435) and Kepler-411 (KIC 11551692) from spot transit mapping, and use a CME deflection model, ForeCAT, to simulate trajectories of hypothetical CMEs launched into the interplanetary medium from Kepler-63 and Kepler-411. We apply the same methodology to the Sun, for comparison. Our results show that in general deflections and rotations of CMEs decrease with their radial velocity and increase with ejection latitude. Moreover, magnetic fields stronger than the Sun’s, such as Kepler-63’s, tend to cause greater CME deflections.

Solar Wind Data Assimilation in an Operational Context: Use of Near‐Real‐Time Data and the Forecast Value of an L5 Monitor

AbstractFor accurate and timely space weather forecasting, advanced knowledge of the ambient solar wind is required, both for its direct impact on the magnetosphere and for accurately forecasting the propagation of coronal mass ejections to Earth. Data assimilation (DA) combines model output and observations to form an optimum estimation of reality. Initial experiments with assimilation of in situ solar wind speed observations suggest the potential for significant improvement in the forecast skill of near‐Earth solar wind conditions. However, these experiments have assimilated science‐quality observations, rather than near‐real‐time (NRT) data that would be available to an operational forecast scheme. Here, we assimilate both NRT and science observations from the Solar Terrestrial Relations Observatory (STEREO) and near‐Earth observations from the Advanced Composition Explorer and Deep Space Climate Observatory spacecraft. We show that solar wind speed forecasts using NRT data are comparable to those based on science‐level data. This suggests that an operational solar wind DA scheme would provide significant forecast improvement, with reduction in the mean absolute error of solar wind speed around 46% over forecasts without DA. With a proposed space weather monitor planned for the L5 Lagrange point, we also quantify the solar wind forecast gain expected from L5 observations alongside existing observations from L1. This is achieved using configurations of the STEREO and L1 spacecraft. There is a 15% improvement for forecast lead times of less than 5 days when observations from L5 are assimilated alongside those from L1, compared to assimilation of L1 observations alone.

Coronal Propagation of Solar Protons during and after Their Stochastic Acceleration

Solar protons in eruptive flares are stochastically accelerated in a wide spatial angle, and then they are effectively kept behind the expanding coronal mass ejection (CME) front, which can either bring protons to the magnetic-field line going to a remote observer or carry them away. We consider 13 solar proton events of cycle 24 in which protons with energy E 100 MeV were recorded and were accompanied by the detection of solar hard X-ray (HXR) radiation with E 100 keV by an ACS SPI detector and γ-radiation with E 100 MeV by the FermiLAT telescope with a source in the western hemisphere of the Sun. The first arrival of solar protons into the Earth’s orbit was determined in each event by a significant “proton” excess over the ACS SPI background during or after the HXR burst. All events were considered relative to our chosen zero time (0 min) of parent flares. The “early” arrival of protons to the Earth’s orbit (+20 min), which was observed in four events, corresponds to the “fast” acceleration of electrons (10 MeV/s). The “late” arrival of protons (+20 min) corresponds to the “slow” acceleration of electrons (1 MeV/s) and was observed in six events. In three events, a “delayed” arrival of protons (+30 min) was observed, when the CME propagation hindered the magnetic connection of the source with the observer. The direction of CME propagation is characterized in the catalog (SOHO LASCO CME Catalog) by the position angle (PA). The observed PA systematizes the times of the first arrival of protons and the growth rate of their intensity. The PA parameter should be taken into account in the analysis of proton events.

Interaction of a coronal mass ejection and a stream interaction region: A case study

We investigated the interaction of a coronal mass ejection (CME) and a coronal hole (CH) in its vicinity using remote-sensing and 1 AU in situ data. We used extreme-ultraviolet images and magnetograms to identify coronal structures and coronagraph images to analyze the early CME propagation. The Wind spacecraft and the Advanced Composition Explorer (ACE) provide plasma and magnetic field data of near-Earth interplanetary space. We applied various diagnostic tools to the images and to the time-series data. We find that the CME erupts under a streamer and causes the evacuation of material at its far end, which is observable as dimming and subsequent CH formation. The CME is likely deflected in its early propagation and travels southwest of the Sun-Earth line. In situ data lack signatures of a large magnetic cloud, but show a small flux rope at the trailing edge of the interplanetary CME (ICME), followed by an Alfvénic wave. This wave is identified as exhaust from a Petschek-type reconnection region following the successful application of a Walén test. We infer that the two spacecraft at 1 AU most likely traverse the ICME leg that is in the process of reconnection along the heliospheric current sheet that separates the ICME and the high-speed stream outflowing from the CH.

Sensitivity of Model Estimates of CME Propagation and Arrival Time to Inner Boundary Conditions

AbstractAccurately forecasting the arrival of coronal mass ejections (CMEs) at Earth is important to enabling mitigation of the associated space weather risks to society. This is only possible with accurate modeling of the event. To do so, we must understand the propagation of a CME through the heliosphere and quantify the performance of models through comparison with spacecraft observations. For the 12 December 2008 Earth‐directed CME event, we compute ensembles using the HUXt solar wind model to analyze CME distortion with a structured solar wind and explore hindcast arrival time error (ATE). By highlighting the impact CME shape has on Root‐Mean‐Square‐Error (RMSE) values, we show that time‐elongation profiles of fronts captured by the Heliospheric Imager (HI) instruments onboard NASA's STEREO mission match those of the modeled CME nose and flank and can therefore be used to infer details of the longitudinal extent of the CME. We then show that accounting for CME distortion is important to enable accurate estimates of the CME arrival at Earth. This can be achieved by either using observations of multiple features in HI data to infer CME evolution or mapping the solar wind back to a lower inner boundary to allow CMEs to be distorted close to the Sun. For the event studied we show that these approaches resulted in reduced RMSEs of 0.73° and 0.64° with an ATE of 1 hour and 3 hours respectively.

Propagation of coronal mass ejections from the Sun to the Earth

Coronal Mass Ejections (CMEs), as they can inject a large amounts of mass and magnetic flux into the interplanetary space, are the primary source of space weather phenomena on the Earth. The present review first briefly introduces the solar surface signatures of the origins of CMEs and then focuses on the attempts to understand the kinematic evolution of CMEs from the Sun to the Earth. CMEs have been observed in the solar corona in white-light from a series of space missions over the last five decades. In particular, LASCO/SOHO has provided almost continuous coverage of CMEs for more than two solar cycles until today. However, the observations from LASCO suffered from projection effects and limited field of view (within 30 Rs from the Sun). The launch in 2006 of the twin STEREO spacecraft made possible multiple viewpoints imaging observations, which enabled us to assess the projection effects on CMEs. Moreover, heliospheric imagers (HIs) onboard STEREO continuously observed the large and unexplored distance gap between the Sun and Earth. Finally, the Earth-directed CMEs that before have been routinely identified only near the Earth at 1 AU in in situ observations from ACE and WIND, could also be identified at longitudes away from the Sun-Earth line using the in situ instruments onboard STEREO. Our review presents the frequently used methods for estimation of the kinematics of CMEs and their arrival time at 1 AU using primarily SOHO and STEREO observations. We emphasize the need of deriving the three-dimensional (3D) properties of Earth-directed CMEs from the locations away from the Sun-Earth line. The results improving the CME arrival time prediction at Earth and the open issues holding back progress are also discussed. Finally, we summarize the importance of heliospheric imaging and discuss the path forward to achieve improved space weather forecasting.

Editorial to the Special Issue “Propagation of Coronal Mass Ejections”

Coronal mass ejections (CMEs) and their associated shocks are one of the main drivers of heliosphere variability, causing both interplanetary and planetary perturbations [...]

Search for Solar Sources of Interplanetary Coronal Mass Ejections Using the Reverse Model of Magnetodynamic Interaction of the Solar Wind in the Heliosphere

In the development and testing of methods for predicting interplanetary coronal mass ejections (ICMEs), it is important to establish their relationship with sources on the Sun—coronal mass ejections (CMEs) observed by coronagraphs. The often used inverse ballistic calculation of the CME onset time does not consider variations in the CME speed when moving through the heliosphere and can give an uncertainty up to a day. With a good accuracy (on the order of ±10 h), the propagation of CMEs in the heliosphere from the Sun to the Earth is described by the model of the magnetodynamic interaction of CMEs with the background solar wind (drag-based model, DBM). In this paper, we propose to search for possible coronal sources of ICMEs, observed near the Earth, using the reverse model of magnetodynamic interaction (reverse DBM, RDBM), which reconstructs in the reverse course the probable propagation of CMEs in the heliosphere and determines their outflow parameters in the solar corona using the measured ICME parameters. The model uses the speed of the background solar wind, which is calculated from the area of coronal holes in the central part of the Sun and presented on the website of the Space Monitoring Data Center of the Skobeltsyn Institute of Nuclear Physics, Moscow State University (SINP MSU), with correction factors.

Assessment of the arrival signatures of the March 2012 CME–CME interaction event with respect to Mercury, Venus, Earth, STEREO-B, and Mars locations

In March 2012, favorable positions of Mercury, Venus, Earth, Mars, and STEREO-B in the inner Solar System provided an opportunity to understand the global structure and the propagation of two coronal mass ejections (CMEs) across the inner Solar System. On 7 March 2012, the Sun ejected two very fast CMEs from the solar active region NOAA AR11489, which were accompanied by two X-class flares. Initialization and subsequent fast expansion from lower coronal heights of flux rope structures were detected as their early eruption signatures in Solar Dynamics Observatory (SDO) observations. White-light observations have been imaged using SOHO/LASCO and STEREO/SECCHI/COR2 and followed from 00:24 UT on 7 March 2012. We examined the kinematics of the reported CMEs and found a significant exchange of momentum and kinetic energy during the interaction, indicating that the collision was almost inelastic. Furthermore, we observed the arrival of this merged CME event at different distances in the inner Solar System and compared the arrival time with other models. The reported event arrived on Mercury at 04:30 UT; Venus, at 13:28 UT on 7 March 2012; and it took roughly 36 h to reach STEREO-B on 08 March, 03:36 UT. The arrivals at Mercury and Venus are observed in the magnetometer measurements onboard MESSENGER and Venus Express (VEx), respectively. A powerful interplanetary shock was observed on 08 March, 10:19 UT at Earth around 30 h after the two X-class flares and CMEs’ eruption. Subsequently, a south-directed interplanetary magnetic field (IMF) was observed on Earth, indicating the arrival of an interplanetary coronal mass ejection (ICME). This event caused the sudden storm commencement and development of one of the major intense geomagnetic storms of SC 24, with a minimum Dst value of −148 nT. The observations by the Mars Express (MEX) mission indicated the arrival of a merged CME ∼2.5 days after its initial observation at Sun. We have analyzed the evolution of these CMEs and their propagation in the inner heliosphere and arrival signatures at four planetary locations. The propagation and arrival signatures are compared to simulations using the WSA-ENLIL + Cone model and the drag-based model at various vantage points. The study showcases the importance of multi-vantage point observations in understanding the propagation of CMEs and their interactions.

Global Sensitivity Analysis and Uncertainty Quantification for Background Solar Wind Using the Alfvén Wave Solar Atmosphere Model

AbstractModeling the impact of space weather events such as coronal mass ejections (CMEs) is crucial to protecting critical infrastructure. The Space Weather Modeling Framework is a state‐of‐the‐art framework that offers full Sun‐to‐Earth simulations by computing the background solar wind, CME propagation, and magnetospheric impact. However, reliable long‐term predictions of CME events require uncertainty quantification (UQ) and data assimilation. We take the first steps by performing global sensitivity analysis (GSA) and UQ for background solar wind simulations produced by the Alfvén Wave Solar atmosphere Model (AWSoM) for two Carrington rotations: CR2152 (solar maximum) and CR2208 (solar minimum). We conduct GSA by computing Sobol' indices that quantify contributions from model parameter uncertainty to the variance of solar wind speed and density at 1 au, both crucial quantities for CME propagation and strength. Sobol' indices also allow us to rank and retain only the most important parameters, which aids in the construction of smaller ensembles for the reduced‐dimension parameter space. We present an efficient procedure for computing the Sobol' indices using polynomial chaos expansion surrogates and space‐filling designs. The PCEs further enable inexpensive forward UQ. Overall, we identify three important model parameters: the multiplicative factor applied to the magnetogram, Poynting flux per magnetic field strength constant used at the inner boundary, and the coefficient of the perpendicular correlation length in the turbulent cascade model in AWSoM.

Turbulence and anomalous resistivity inside near-Earth magnetic clouds

ABSTRACT We use in situ data from the Wind spacecraft (https://wind.nasa.gov/) to survey the amplitude of turbulent fluctuations in the proton density and total magnetic field inside a large sample of near-Earth magnetic clouds (MCs) associated with coronal mass ejections (CMEs) from the Sun. We find that the most probable value of the modulation index for proton density fluctuations (δnp/np) inside MCs ranges from 0.13 to 0.16, while the most probable values for the modulation index of the total magnetic field fluctuations (δB/B) range from 0.04 to 0.05. We also find that the most probable value of the Mach number fluctuations (δM) inside MCs is ≈0.1. The anomalous resistivity inside the near-Earth MCs arising from electron scattering due to turbulent magnetic field fluctuations exceeds the (commonly used) Spitzer resistivity by a factor of ≈500–1000. The enhanced Joule heating arising from this anomalous resistivity could impact our understanding of the energetics of CME propagation.

Modeling of Solar Wind Disturbances Associated with Coronal Mass Ejections and Verification of the Forecast Results

Solar wind (SW) disturbances associated with coronal mass ejections (CMEs) cause significant geomagnetic storms, which may lead to the malfunction or damage of sensitive on-ground and space-based critical infrastructure. CMEs are formed in the solar corona, and then propagate to the Earth through the heliosphere as Interplanetary CME (ICME) structures. We describe the main principles in development with the online, semi-empirical system known as the Space Monitoring Data Center (SMDC) of the Moscow State University, which forecasts arrival of ICMEs to Earth. The initial parameters of CMEs (speeds, startup times, location of the source) are determined using data from publicly available catalogs based on solar images from space telescopes and coronagraphs. After selecting the events directed to Earth, the expected arrival time and speed of ICMEs at the L1 point are defined using the Drag-Based model (DBM), which describes propagation of CMEs through the heliosphere under interaction with the modeled quasi-stationary SW. We present the test results of the ICME forecast in the falling phase of Cycle 24 obtained with the basic version of SMDC in comparison with results of other models, its optimization and estimations of the confidence intervals, and probabilities of a successful forecast.

Magnetohydrodynamic simulation of coronal mass ejections using interplanetary scintillation data observed from radio sites ISEE and LOFAR

Interplanetary scintillation (IPS) is a useful tool for detecting coronal mass ejections (CMEs) throughout interplanetary space. Global magnetohydrodynamic (MHD) simulations of the heliosphere, which are usually used to predict the arrival and geo-effectiveness of CMEs, can be improved using IPS data. In this study, we demonstrate an MHD simulation that includes IPS data from multiple stations to improve CME modelling. The CMEs, which occurred on 09–10 September 2017, were observed over the period 10–12 September 2017 using the Low-Frequency Array (LOFAR) and IPS array of the Institute for Space-Earth Environmental Research (ISEE), Nagoya University, as they tracked through the inner heliosphere. We simulated CME propagation using a global MHD simulation, SUSANOO-CME, in which CMEs were modeled as spheromaks, and the IPS data were synthesised from the simulation results. The MHD simulation suggests that the CMEs merged in interplanetary space, forming complicated IPS g-level distributions in the sky map. We found that the MHD simulation that best fits both LOFAR and ISEE data provided a better reconstruction of the CMEs and a better forecast of their arrival at Earth than from measurements when these simulations were fit from the ISEE site alone. More IPS data observed from multiple stations at different local times in this study can help reconstruct the global structure of the CME, thus improving and evaluating the CME modelling.

A Semi-empirical Approach to the Dynamic Coupling of CMEs and Solar Wind

Coronal mass ejections (CMEs) are one of the most relevant phenomena for space weather. Moreover, CMEs can negatively affect essential services and facilities. Therefore, to protect society, we require well-grounded knowledge of the physics that governs the propagation of CMEs from near the Sun to the orbit of Earth. In this work, we deduce expressions to approximate the main forces that affect the dynamic coupling between CMEs and the surrounding solar wind. Therefore, we explore the CME–solar wind dynamic coupling from a magnetohydrodynamic perspective, which, combined with a few reasonable assumptions, allows us to obtain expressions for the thermal and magnetic pressure forces, viscous and dynamic drag, and gravity. We simultaneously use our expressions to compute the trajectories of 34 Earth-directed CMEs. Our results, which are compared with in situ data, show significant quantitative consistency; our synthetic transits closely mimic their in situ observed counterparts. We conclude from our results that magnetic, thermal, and dynamic drag significantly surpass the other forces such as dynamic agents of CMEs in the interplanetary medium. In addition, we find that the initial relative speed of CMEs and solar wind is a determinant factor for the dynamic behavior of CMEs. In other words, subsonic CMEs are initially mostly affected by magnetic and thermal pressure forces, whereas super-magnetosonic CMEs are initially governed by inertial drag.

Magnetohydrodynamic Simulation of Multiple Coronal Mass Ejections: An Effect of “Pre-events”

Coronal mass ejections (CMEs) are a major source of solar wind disturbances that affect the space plasma and magnetic field environment along their propagation path. Accurate prediction of the arrival of a CME at Earth or any point in the heliosphere is still a daunting task. In this study we explore an often overlooked factor—the effects of “pre-events” that can alter the propagation of a CME due to a preceding CME. A data-driven magnetohydrodynamic numerical model is used to simulate the propagation of multiple CMEs and their driven shocks that occurred in 2012 July. The simulation results are validated with in situ solar wind plasma and magnetic field measurements at 1 au, testing the appropriateness of our simulation results for interpreting the CME/shock evolution. By comparing the simulation results with and without preceding CMEs, we find that the trailing CME can be accelerated by the “wake” of a preceding CME. A detailed analysis suggests that the acceleration is caused partially by an increase in the background solar wind and partially by the so-called “snowplow” effect, with the latter being the major contributor for the 2012 July event.

Time‐of‐Arrival of Coronal Mass Ejections: A Two‐Phase Kinematics Approach Based on Heliospheric Imaging Observations

AbstractThe forecasting of the Time‐of‐Arrival (ToA) of coronal mass ejections (CMEs) to Earth does not yet meet most Space Weather users' requirements. The main physical reason is our incomplete understanding of CME propagation in the inner heliosphere. Therefore, many ToA forecasting algorithms rely on simple empirical relations to represent the interplanetary propagation phase using, mostly, kinematic information from coronagraphic observations below 30 solar radii (Rs) and a couple rather simplifying assumptions of constant direction and speed for the transient. We replace the assumption of constant speed in the inner heliosphere with a two‐phase behavior consisting of a decelerating (or accelerating) phase from 20 Rs to some distance, followed by a coasting phase to Earth. In a nod toward a forecasting scheme, we consider Earth‐directed CMEs, use kinematic measurements only from the Heliospheric Imagers aboard both STEREO spacecraft, treat each spacecraft separately to increase the event statistics, analyze the measurements in a data‐assimilative fashion, and intercompare them against three localization schemes for single viewpoint observations (fixed‐φ, harmonic mean and self‐similar expansion). For the 21 cases, we obtain the best mean absolute error (MAE) of 6.4 ± 1.9 hr. In fact, the difference between calculated and observed ToA is <52 min for 42% of the cases that return plausible ToA estimates. We find that some CMEs continue to decelerate beyond even 0.7 AU but reasonable forecasts should be possible with 31 hr lead time. This work is a proof‐of‐concept and an analysis of a larger event sample is required to fully validate this technique.

ICARUS, a new inner heliospheric model with a flexible grid

Context. Simulating the propagation and predicting the arrival time of coronal mass ejections (CMEs) in the inner heliosphere with a full three-dimensional (3D) magnetohydrodynamic (MHD) propagation model requires a significant amount of computational time. For CME forecasting purposes, multiple runs may be required for different reasons such as ensemble modeling (uncertainty on input parameters) and error propagation. Moreover, higher resolution runs may be necessary, which also requires more CPU time, for example for the prediction of solar energetic particle acceleration and transport or in the framework of more in-depth studies about CME erosion and/or deformation during its evolution. Aims. In this paper we present ICARUS, a new inner heliospheric model for the simulation of a steady background solar wind and the propagation and evolution of superposed CMEs. This novel model has been implemented within the MPI-AMRVAC framework which enables the use of stretched grids and solution adaptive mesh refinement (AMR). The usefulness and efficiency (speed-up) of these advanced features are explored. In particular, we model a typical solar wind with ICARUS and then launch a simple cone CME and follow its evolution. We focus on the effect of radial grid stretching and two specific methods or criteria to trigger solution AMR on this typical simulation run. Methods. For the solar background wind simulation run, we limited the mesh refinement to the area(s) of interest, in this case a co-rotating interaction region (CIR). For the CME evolution run, on the other hand, we apply AMR where the CME is located by the use of a tracing function. As such, the grid is coarsened again after the CME has passed. Results. The implemented AMR is flexible and only refines the mesh in a particular sector of the computational domain, for example around the Earth or a single CIR, and/or for a particular feature such as CIR or CME shocks. Radial grid stretching alone yields speed-ups of up to 4 and more, depending on the resolution. Combined with solution adaptive mesh refinement, the speed-ups can be much larger depending on the complexity of the simulation (e.g., number of CIRs in the background wind, number of CMEs) and on the chosen AMR criteria, thresholds and the number of refinement levels. Conclusions. The ICARUS model implemented in the MPI-AMRVAC framework is a new inner heliospheric 3D MHD model that uses grid stretching as well as AMR techniques. The flexibility in the grid and its resolution allows an optimization of the computational time required for CME propagation simulations for both scientific and forecasting purposes.

Determination of coronal mass ejection orientation and consequences for their propagation

Context. The configuration of the interplanetary magnetic field and features of the related ambient solar wind in the ecliptic and meridional plane are different. Therefore, one can expect that the orientation of the flux-rope axis of a coronal mass ejection (CME) influences the propagation of the CME itself. However, the determination of the CME orientation, especially from image data, remains a challenging task to perform. Aim. This study aims to provide a reference to different CME orientation determination methods in the near-Sun environment. Also, it aims to investigate the non-radial flow in the sheath region of the interplanetary CME (ICME) in order to provide the first proxy to relate the ICME orientation with its propagation. Methods. We investigated 22 isolated CME-ICME events in the period 2008–2015. We determined the CME orientation in the near-Sun environment using the following: (1) a 3D reconstruction of the CME with the graduated cylindrical shell (GCS) model applied to coronagraphic images provided by the STEREO and SOHO missions; and (2) an ellipse fitting applied to single spacecraft data from SOHO/LASCO C2 and C3 coronagraphs. In the near-Earth environment, we obtained the orientation of the corresponding ICME using in situ plasma and field data and also investigated the non-radial flow in its sheath region. Results. The ability of GCS and ellipse fitting to determine the CME orientation is found to be limited to reliably distinguish only between the high or low inclination of the events. Most of the CME-ICME pairs under investigation were found to be characterized by a low inclination. For the majority of CME-ICME pairs, we obtain consistent estimations of the tilt from remote and in situ data. The observed non-radial flows in the sheath region show a greater y direction to z direction flow ratio for high-inclination events, indicating that the CME orientation could have an impact on the CME propagation.